Changed snap toolbar behaviour:
- create a list of available snaps (Gui.Snapper.snaps)
- make it consistent with Snap Gui Commands (in gui_snaps module)
- create a list of active snaps (Gui.Snapper.active_snaps)
- refactor the isEnabled() method to allow it to check if the given snap is in Gui.Snapper.active_snaps and not if the snap toolbar button isChecked()
- updated and reordered the new list of gui snap commands in draftutils.init_tools and used it as a base to refactor the creation of draft toolbar
- updated all the draft snap gui tools to make them control the toolbar buttons directly
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And do not load the `Snapper` in `DraftGui`.
The Snapper should be initialized by the module
that imports `DraftGui`, most probably `DraftTools`
or even by the `InitGui` of the workbench.