Rewrite dream settings.

The available dreams will now be shown in a grid, with a preview button
at the bottom.

Screenshot (white placeholder image used):
http://screen/6pe6EoACPoQN8TZ.png
http://screen/4nR6Wg5pN7pL6Wb.png

Phone (single column layout):
http://screen/4WFqzZR8Yf9H3VZ.png

Colors and margins will be finalized once final mocks are done.

Bug: 207681076
Bug: 214250590
Test: locally on device
Change-Id: Ie68bdc60e74e72dc3c3cee3f1ffd40f5613109b9