Rename Index into History

- changes in privly-chrome for renaming Index into History
- changed Chrome context menu:
   'Privly Content Extension' -> 'Privly', 
   'ZeroBin' -> 'New encrypted message - ZeroBin', 
   'PlainPost' -> 'New unencrypted message - PlainPost', 
Let's remove the history application from the context menus.