Import Android color picker module (https://code.google.com/p/android-color-picker/).
Remove unreferenced and empty XML file (previously used for preferences).
Refactor WHATSAPP_PACKAGE_NAME to keep the value DRY.
Initial version of highlight groups feature. Fixes #8.
Add preferences for the highlight feature.

Also refactor what is already there into groups.
Increment version in preparation for release.