Remember editor expansion state on rotates (E10)

* Prompt user about discarding changes when back pressed
  on editor (regressed in E5)
* Show a toast and close when no editors (i.e. input
  fields) can be bound.
* Try to clarify the different behavior of
  CompactSectionSectionView for names and groups.

Bug 23589603

Change-Id: If045ddb6d839574dc4109195b0d8841cd6083561