FEM: update imports in coding conventions

src/Mod/Fem/coding_conventions.md

@@ -1,6 +1,7 @@
 # FEM coding_conventions
 These coding rules apply to FEM module code only. Other modules or the base system may use different coding rules especially in naming policy of Python.
 
+
 ## Spelling
 - Be mindful of spelling. Spell checks are quite often neglected.
 - Utilize [codespell](https://github.com/codespell-project/codespell) to discover and quickly correct spelling errors.  
@@ -17,6 +18,7 @@ These coding rules apply to FEM module code only. Other modules or the base syst
   2) To find the most amount of typos we recommend running a quick `pip install --upgrade`  
   See the [codespell docs](https://github.com/codespell-project/codespell#updating) for more info.
 
+
 ## Python and C++
 ### Code formatting
 - All files should have a license header
@@ -43,9 +45,10 @@ These coding rules apply to FEM module code only. Other modules or the base syst
 
 ### Imports
 - Only one import per line.
-- Even on import from some_module import something. There should only be one something per line.
+    - on import from 'some_package' import 'some_module'. There should only be one 'some_module' per line.
+    - on import from 'some_module' import 'some_method'. There should only be one 'some_method' per line.
 - Each import group should be sorted alphabetically.
-- First the import some_module ones, afterwards the from some_module import something.
+- First the 'import some_module' ones, afterwards the 'from some_module import something'.
 - First absolute path imports than relative path imports.
 - On relative path imports first the one dot ones, afterwards the two dot ones.
 - Star import should not be used at all (from some_module import *).
@@ -54,18 +57,25 @@ These coding rules apply to FEM module code only. Other modules or the base syst
     - One empty line
     - Third-party imports
     - One empty line
-    - FreeCAD-specific imports from module FreeCAD
-    - One empty line
-    - Other FreeCAD non Gui imports
-    - One empty line
+    - non Gui FreeCAD specific imports
+        - from module FreeCAD
+        - One empty line
+        - other modules, but not FEM
+        - One empty line
+        - FEM specific imports
+            - absolute imports
+            - One empty line
+            - relative imports
+        - One empty line
     - FreeCAD Gui imports: 
         - The import of Gui modules should be guarded by a 'if FreeCAD.GuiUp:'
         - On Gui only modules the guard is not needed
-        - Same as above but without an empty line
+        - Same as above but without a empty line
         - Standard library imports
         - Third-party Gui imports
         - FreeCAD-specific imports from module FreeCADGui
         - other FreeCAD Gui imports
+        - FEM Gui imports
 - The above paragraphs highly reduces merge conflicts.
 
 ### Naming policy
@@ -117,6 +127,7 @@ Python style is preferred over Doxygen style
     - if this is not available the object can not even created
     - if task panel is separate the object can be createdh
 
+
 ## C++
 ### Naming policy
 - CamelCase names
@@ -126,6 +137,7 @@ Python style is preferred over Doxygen style
     - Do not use to many slashes in a row. This could cause trouble with Doxygen.
     - see [PR with comment](https://github.com/FreeCAD/FreeCAD/pull/2757#discussion_r355218913)
 
+
 ## Icons
 ### Naming plicy
 - Command icons use the command name.