Add Slices Data object and DB Contract

Add Slices Data object and DB Contract

Add in a Data object used to represent one row
in a new SQLite database used for building Slices.

The database has the following schema:
- Key
- Title
- Subtitle
- Screentitle
- Icon
- Fragment
- Controller

The key is the preference key.
Title, subtitle and Icon are for UI info.
Screentitle and fragment are for the intent.
Controller is used to get dynamic ui info (like summary),
and to take actions on the slice (like a toggle).

The actual indexing and a Slice will be handled in a subsquent CL,
but a prototype can be found here: ag/3324435

Test: robotests
Bug: 67996923
Change-Id: Id91deb58a3ab89ce1dab5a3f34cdb9ade6263aa8