Added tool bits concept and some initial templates

src/Mod/Path/Tools/.gitignore

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+*.fcstd1
+*.FCStd1

src/Mod/Path/Tools/README.md

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+# Tools
+
+Each tool is stored as a JSON file which has the template's path and values for all named constaints of the template.
+It also includes all additional parameters and their values.
+
+When a tool is instantiated in a job the PDN body is created from the template and the constraints are set according
+to the values from the JSON file. All additional parameters are created as properties on the object. This provides a
+body with the correct shape and dimensions which can be used to generate a point cloud or mesh for advanced algorithms
+(and potentially simulation).
+
+# Tool Libraries
+
+Due to each tool being stored in its own file and the storage/organization of those files being quite flexible the
+importance of a tool library for organisational purposes is quite diminished. The user is free to organise their tools
+in whichever directory hierarchy they see fit and can also name them as best fits their use and organisation. A
+_tool library_ is nevertheless a great representation for a physical grouping of tools, such as in an automatic tool
+changer.
+
+A tool library is a (JSON) file with a mapping of tool id to the path of the tool file. As a consequence each tool
+can be in multiple libraries and doesn't have an `id` of it's own. The `id` is a property of the library.
+
+If a tool from a tool library (or an entire tool library) is added to a job it retains its `id` from the library as a
+property. Adding a tool bit directly rsults in the tool getting the next free id assigned.
+
+# Tool Controllers
+
+They largely stay the same as they are today. As an additional feature it should be possible to _copy_ a TC, which
+allows for easy feed/speed changes for the same tool.
+
+Abover requirement highlights one change though, that the `id` should be a property of the Bit, and not of the TC.
+There are two requirements that are currently mapped to a single `id`. There needs to be an identification of which
+TC is being used by a certain op, and which tool number to use for a `M6` command.
+
+# Paths and Extensibility
+
+The following directory structure is used for supplied (shipped with FreeCAD) tools:
+```
+  Tools
+    + Bit
+    + Library
+    + Template
+```
+Strictly speaking a user is free to store their tools wherever they want and however they want. By default the file
+dialog will open the corresponding directory (depending on context), or whichever directory the user opened last.
+
+Above directory structure with the most common default tools shipped with FreeCAD should be installed analogous to
+TechDraw's templates.
+
+## How to create a new tool
+
+1. Set the tool's Label, this will show up in the object tree
+1. Select a tool shape from the existing templates. If your tool doesn't exist, you'll have to create a new template,
+   see below for details.
+1. Each template has its own set of parameters, fill them with the tool's values.
+1. Select additional parameters
+1. Save the tool under the name that makes sense to you
+
+
+## How to create a new tool bit Template
+
+A tool bit template represents the physical shape of a tool. It does not completely desribe the bit, for that some
+additional parameters are needed which will be added when an actual bit is parametrized from the template.
+
+1. Create a new FreeCAD document
+1. Open the `PartDesign` workbench, create a body and give the body the name you want to show up in the bit selection.
+1. Create a sketch in the XZ plane and draw half the profile of the bit.
+   * Put the top center of the bit on the origin (0,0)
+1. For any constraint serving as a parameter for the tool (like overall Length) create a named constraint
+   * The name is the label of the input field
+   * Names are split at CamelCase boundaries into words in the edit dialog
+   * Use a `;` in the name to add help text which will show up as the entry fields tool tip
+   * If the tool is used by legacy ops it should at least have one constraint called `Diameter`
+   * Use construction lines for constraints that are not directly accessible, like `Diameter` and `Angle`
+1. Any unnamed constraint will not be editable for a specific tool
+1. Once the sketch is fully constrained, close the sketch
+1. Rotate the sketch around the z-axis
+1. Save the document as a new file in the Template directory
+   * Before saving the document make sure you have _Save Thumbnail_ selected, and _Add program logo_ deselected in
+     FreeCAD's preferences.
+   * Also make sure to switch to _Front View_ and _Fit content to screen_
+   * Whatever you see when saving the document will end up being the visual representation of the template