Travis CI builds

* Added .travis.yml that does the following:
  * creates an avd
  * starts an emulator
  * waits for the emulator to start
  * sets up the android sdk and the required components (with the needed license)
  * builds the source code
  * uploads the built artifact (apk) to github releases (only if a git tag was created for the same)
updating the github encrypted key
Added USBPower commands for proper xperia Ray functionality. MUST HAVE
ROOT ACCESS.
Switched back to standard USBPower commands, sorry pushed to wrong
branch!
Merge pull request #17 from virmani/master

Using gradle build system.
Merge branch 'travis_builds'
update travis.yml for nightscout's repo