Add -DEBUG suffix to the version name. Changes to build.gradle to support

This adds versionCode and versionName to the build.gradle file. They are supposed to overwrite those two values in the AndroidManifest on build, and should therefore be changed in the build.gradle from now on.

This allows the use of versionNameSuffix in the debug configuration to append "-DEBUG" or any other string to the version name attribute. Instead of 1.5.3 on the version name for debug builds, it will say 1.5.3-DEBUG.