Added a fix for the main menu getting removed every time the application is closed
Removed incorrect comment
Added example of how to replace the model factory (commented out)
Fixed the bug where contributed menu items are added everytime the application is run
Renamed menu ids to the standard Eclipse ids, so that contributed menu items work
Replacing ShowView dialog with E4 version (closes #39 #38)
Added an addon filter that removes unwanted parts from the application model