Upgrade gradle-android-plugin to 0.7

Unfortunately this results in some duplicated code because buildConfig
was changed to work on individual fields with buildConfigField so you
can't construct the value in a method.
Fix DEV_SERVER in release

Turns out you need to pass in a string that contains 2 double quotes.
Update build tools and gradle plugin

Might as well.
Merge upgrade-gradle-android-plugin (#186) into master

Upgrade gradle-android-plugin to 0.8

Unfortunately this results in some duplicated code because buildConfig
was changed to work on individual fields with buildConfigField so you
can't construct the value in a method.