Misc. typos

+ some are doxy others are just comment code.  
+ some minor whitespace and grammatical tweaks. 
+ app/SCL/* typos have also been submitted upstream (https://github.com/stepcode/stepcode/pull/366). So it's ok to merge them in to master.

src/Mod/Spreadsheet/App/PropertySheet.cpp

@@ -974,7 +974,7 @@ void PropertySheet::addDependencies(CellAddress key)
 }
 
 /**
-  * Remove dependecies given by \a expression for cell at \a key.
+  * Remove dependencies given by \a expression for cell at \a key.
   *
   * @param expression Expression to extract dependencies from
   * @param key        Address of cell containing the expression