- move required contract for adapter into DynamicGridAdapterInterface so implementers can swap out the adapter completely;
- add listener callback for enter/exit edit mode;
- remove inner long click listener (not need) and update startEditMode(int) method;
- add ability to disable edit mode;
- update example app
Merge branch 'master' of https://github.com/askerov/DynamicGrid

Conflicts:
	dynamicgrid/src/org/askerov/dynamicgrid/AbstractDynamicGridAdapter.java
	dynamicgrid/src/org/askerov/dynamicgrid/DynamicGridView.java
Merge branch 'master' of https://github.com/askerov/DynamicGrid

Conflicts:
	dynamicgrid/src/org/askerov/dynamicgrid/AbstractDynamicGridAdapter.java
	dynamicgrid/src/org/askerov/dynamicgrid/DynamicGridView.java