Leverage the panel title font size of non-first row

The title of non-first row in a slice has smaller font size by default.

- Sync the font size with the one of the first row.
- Also rename the related styles in style.xml
- Let homepage slices has smaller font on non-first row based on UX
  design.

Bug: 152831413
Test: visual
Change-Id: I87c2008745adb68c031dc2d4e15b93bccfea12b0