Misc typos and whitespace fixes

Found via `codespell -q 3 -I ../fc-word-whitelist.txt -S ./.git,*.po,*.ts,./ChangeLog.txt,./src/3rdParty,./src/Mod/Assembly/App/opendcm,./src/CXX,./src/zipios++,./src/Base/swig*`

src/App/Expression.cpp

@@ -165,7 +165,7 @@ void UnitExpression::setUnit(const Quantity &_quantity)
 }
 
 /**
-  * Evaulate the expression
+  * Evaluate the expression
   *
   * @returns A NumberExpression set to 1.0.
   */