Added Plugins as an parameter to the slick grid constructor call and added a OnPostInit event.

Plugins are needed to be part of constructor call so that they can be
registered before and if needed plugins can subscribe to the PostInit
event
PostInit event is raised one time - just before Init finishes
Merge branch 'master' into Feature-postInit
Merge branch 'Feature-slickgrid-menu' into Feature-postInit