Use gradle plugin 0.7.+ and wrapper 1.9.

Necessary for versions of Android Studio >= 0.4.0.
Remove versionCode, versionName, minSdkVersion, and targetSdkVersion attributes.

They are determined from the values in build.gradle.
Support minSdkVersion 7.
Mark assorted fields as "final" where appropriate.
Remove unnecessary initialisation of proposedEdgeColor.