remove vtm-android-app submodule
gradle: use android build-tools 20.0
update README
fix travis build
avoid network on main-thread exception with OkHttp
cannot test OkHttp close atm
wraps closing inputStream in thread to prevent Network On Main Thread Exception when exiting MapActivity
implements okhttp response caching
Adds circle.yml

Enable Cicle CI integration and display build status in README.md
updates build tools