Fixes to get the plugin compiled with MSVC 2010 and Qt 5.3.1 (getting ready for release)...
Added Project level mistakes as a Navigation Widget.

A navigation widget was added to show all files with the number of spelling mistakes in each of the files. Clicking on any of the items in the list will open the relevant file.
Cleanup of Core after adding project model.

Removed the QHash that was replaced with the new model.
Cleanup after adding Navigation Widget.

- The project action was removed from the toolbar since this was not needed any more.
- Removed showing the file name in the output pane since all mistakes in the pane should be for the open file. It was not adding any value. The way of handling the project wide mistakes was rethought.
Forgot to update the column names after the previous commit.
Spellchecked the sources (testing the plugin).