Use less icons in hotseat when in 3 button nav for tablet

- We have less space on tablets when 3 button nav is enabled because QSB is now inline with the icons. This creates a new attribute to define how many icons should be shown when in that mode. This could be used for other grids in the future as well.
- InvariantDeviceProfile now listens for nav mode changes

Fixes 214882090, 221420204
Test: manual

Change-Id: I012432a1a322c4e5505e46a1198c841ab124aaa6