Misc. typos and whitespace

Found via `codespell -q 3 --skip="*.po,*.ts,./.git,./src/3rdParty,./src/CXX,./src/zipios++,./src/Mod/Assembly/App/opendcm,./ChangeLog.txt" -I ../fc-word-whitelist.txt` and `grep`. Excess whitespace auto-removed by Atom editor.

src/Mod/Fem/femguiobjects/_ViewProviderFemResultMechanical.py

@@ -44,7 +44,7 @@ import numpy as np
 
 
 class _ViewProviderFemResultMechanical:
-    "A View Provider for the FemResultObject Python dervied FemResult class"
+    "A View Provider for the FemResultObject Python derived FemResult class"
 
     def __init__(self, vobj):
         vobj.Proxy = self

src/Mod/Fem/femmesh/meshtools.py

@@ -1152,7 +1152,7 @@ def get_ref_facenodes_areas(femnodes_mesh, face_table):
 
 def get_ref_shape_node_sum_geom_table(node_geom_table):
     # shape could be Edge or Face, geom could be length or area
-    # sum of legth or area for each node of the ref_shape
+    # sum of length or area for each node of the ref_shape
     node_sum_geom_table = {}
     for n, A in node_geom_table:
         # print(n, ' --> ', A)

src/Mod/Fem/femobjects/_FemResultMechanical.py

@@ -65,7 +65,7 @@ class _FemResultMechanical():
     # standard Feature methods
     def execute(self, obj):
         """"this method is executed on object creation and whenever the document is recomputed"
-        update Part or Mesh should NOT lead to recompution of the analysis automatically, time consuming
+        update Part or Mesh should NOT lead to recomputation of the analysis automatically, time consuming
         """
         return