Sheet: Make ViewProviderSpreadsheet.h self-contained

and fix a few minor issues

src/Mod/Spreadsheet/Gui/ViewProviderSpreadsheetPyImp.cpp

@@ -23,7 +23,6 @@
 #include "PreCompiled.h"
 
 // clang-format off
-#include "SpreadsheetView.h"
 #include "ViewProviderSpreadsheetPy.h"
 #include "ViewProviderSpreadsheetPy.cpp"
 // clang-format on
@@ -56,7 +55,6 @@ PyObject* ViewProviderSpreadsheetPy::getCustomAttributes(const char* /*attr*/) c
     return nullptr;
 }
 
-
 int ViewProviderSpreadsheetPy::setCustomAttributes(const char* /*attr*/, PyObject* /*obj*/)
 {
     return 0;