Multiple fixes from google/iosched

Fix for 20.0.0 build tools bug

reference: https://code.google.com/p/android/issues/detail?id=77629

Update travis.yml for lollipop

Updated build-tools to rev 21.0.1
Updated android component, image and target to 21

Update build tools rev 21.0.2

Updated build tools to rev 21.0.2 in android build.gradle, building doc and travis.yml
This rev. solves the windows users issue:
https://code.google.com/p/android/issues/detail?id=77629

Travis wont work until they upgrade or you install 23.0.5 sdk manually,
emulator or something i dont know do. I ll wait your/their solution.
http://docs.travis-ci.com/user/languages/android/
https://github.com/travis-ci/travis-cookbooks/blob/master/ci_environment/android-sdk/CHANGELOG.md

Update to v21 SwipeRefreshLayout. Also fix nav drawer BACK button bug.

Change-Id: I13a0880240c4d49b2fdca5948594567332ca8aaf