lint: add rules

Signed-off-by: KhasMek <Boushh@gmail.com>
drawables: final cleanup and polish

  -Remove last unneeded placeholders
  -Add drawables for missing densities
  -Correct AR on some drawables
  -Move .9.png's out of drawable (image drawables
    don't belong there).

Signed-off-by: KhasMek <Boushh@gmail.com>
About: add version number

Signed-off-by: KhasMek <Boushh@gmail.com>
tutorial: materialize

Signed-off-by: KhasMek <Boushh@gmail.com>