Add dynamic summaries to Slices

Summary on slices will now determined by checking that
summaries in the following order are valid:
1) SliceData summary
2) Preference Controller summary
3) SliceData screen title

Valid is currently defined as:
- Not empty / null
- Not whitespace
- Not sumamry placeholder

Fixes: 71640678
Test: robotests
Change-Id: I5e699e8566ece80742d311617b7dc4e9a9bda8cf