Initial changes for a export wizards

Introduces the native project wizard. In addition to the wizard project
generators are now extension points. Wizard provides option to export a
platform specific project only if a project generator extension point is
available for it.
Save dialog settings 

History of used destination directories are now saved and restored
Make generation on a Job

Moves the generation of the native projects to a Job. Introduces
NativeProjectExportOperation.java which implements the logic for running
the AbstractProjectGeneratorDelegates per platform & project pair.
Project generator extension point supports expression based enablement

This adds the expression based enablement to the project generators.
Also ProjectGeneratorContentProvider is adjusted to filter disabled
Project generators. iOS implementation now filters if not running on Mac
OSX
Overwrite files query for native project export wizard

The implementation for the IOverwriteQuery interface is completed and
bow the NativeProjectExportOperation is also utilizing the interface.
Change to use WorkbenchLabelProvider

Since HybridProject implements IAdaptable interface now we no longer
need our own label providers. HybridProjectLabelProvider is removed.
Also iOS and Android launch configuration UIs are updated to use
WorkbenchLabelProvider
Images for native project export wizard

Adds the banner image and the wizard icon for native project export
wizard
Extension point for platform images

Adds a new extension point for defining platform images. Implements the
PlatformImages extension point for Android & iOS. Also adds the icons
for launch shortcuts.
Merge branch 'export_wizards'