[doc] Clarify property file location in README
Use apt gradle plugin for annotation processing dependencies

Notably suppresses lint errors about auto-generated classes.
Annotate API compatibility helper methods with targeted API version

Suppresses lint errors regarding incompatible APIs.
[strings] Remove unused strings.
[ui] Change to root layout to merge layout.
[ui] Add image content description for accessibility
Remove unused resources.
Merge branch 'fix/lint_fixes'