Bottom nav bar and screen transitions

[nahwneeth]

• Added slide in and out screen transitions.
• Removed multiple BottomAppBarAll.
• Added BottomNavActivity which holds the bottom navigation bar and uses a second NavHost to shows the screens.
• Updated drawer to not open inbox, saved & profile as new screens.
• CommunityListAcitivity does not show bottom nav bar when selecting a community for creating a post.
• Tapping multiple times on a bottom nav tab doesn't open multiple views.

• The selected icon is filled and the others are outlined.
• Both the bottom nav bar and the navigation bar below it will always have the same color.
• Back button isn't shown for screen opened from the bottom nav bar.

• Fixed the bottom nav bar padding rising with the keyboard.

Closes #714
Closes #830

PS: This isn't a huge commit. The home activity has one less indent coz drawer was moved.

[twizmwazin]

This change seems to conflict with the "Show navigation bar" option in settings. If this setting is disabled, there doesn't seem to be a way to navigate from search/inbox/saved/profile back to the home page. There is no back or drawer indicator on the page, and hitting back just exits the app.

[nahwneeth]

I've restored the back button if bottom nav bar isn't shown.