Update project files for Java 1.7 syntax support

[rickbrew]

I believe there's something we need to declare in gradle.properties and/or elsewhere. So let's figure that out.

[jasta]

Diamond syntax FTW!

[clemp6r]

You have to add the following in the android section of your build.gradle:

compileOptions {
    sourceCompatibility JavaVersion.VERSION_1_7
    targetCompatibility JavaVersion.VERSION_1_7
}