Allow more customization of the action bar

[ryanmoelter]

We should allow people to specify whether they want to use the space under the action bar / nav bar / status bar and allow for making those areas transparent or translucent. Additionally, it would be nice to make it extensible enough for people to use it to modify other things that might live outside screens (fab, bottom nav, etc.)

[ryanmoelter]

Also, we should provide a default implementation