Added Translation documentation.  APPTENTIVE-3022
Merge pull request #14 from apptentive/trans

Added Translation documentation.  APPTENTIVE-3022
Remove outdated section on the Hidden Messages page.

APPTENTIVE-3340
Merge pull request #15 from apptentive/APPTENTIVE-3340

Remove outdated section on the Hidden Messages page. APPTENTIVE-3340
Merge pull request #16 from apptentive/master

Merge master into android
Rename customization_guide.md to customization.md
Replace customization stub section with link to actual customization page.