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.
Merge pull request #12 from nikclayton/master

Support SDK Version >=7, and assorted cleanups