UX Fixes for Settings Panels

UI Fixes include:
- Fix height of bottom bar
- Fix start / end padding of See More and Done buttons
- Remove scroll shadow in recycler view
- Consolidate most layout code into a single file, only
separating the distinguished elements into the landscape file.

I cannot fix b/126731930 until a Slice bug is fixed, where the top
padding is applied to the bottom of sliceview instead.

Fixes: 126720235
Fixes: 126720220
Fixes: 126720167
Test: manual inspection & layout inspector

Change-Id: I6e3434aabe221134e7278f92bab34122719c179a