CB-3445: Add an initial set of Gradle build scripts

These scripts will build an android project, in debug and release mode.
They also support additional library projects, such as Crosswalk, being
added to libraries.gradle (and settings.gradle). A flag can be set in
libraries.gradle to enable multi-architecture builds.

bin/templates/project/libraries.gradle

@@ -0,0 +1,7 @@
+dependencies {
+// This file contains no plugins by default.
+// To add a third-party library project, add a line to this file like
+//    compile project(':library_dir_name')
+}
+// If multiple ndk architectures are provided, uncomment this line
+//ext.multiarch=true