Android SDK: Bug fixes and Version Updates

- store helper scripts out of android sdk directory
  (fix travis-ci/travis-ci#2279)

- change license pattern in android-update-sdk helper script
  (fix travis-ci/travis-ci#2466)

- upgrade to Android SDK 23 and use new system images identifiers

- ship android-wait-for-emulator helper script
  (usage to be described in docs.travis-ci.com)

Note: maven-rescue recipe is still a work in progress, and for this
reason it is disabled for now.
Android SDK: accept all the licenses by default

Related to travis-ci/travis-ci#2296 and travis-ci/travis-ci#2466
Bump foodcritic to validate the use of git lwrp
Don't show Foodcritic warnings
Update changelog (Android SDK updates and fixes)
Don't preinstall API 4.4W (android-20)

These components were not part of previous VM image.
Merge pull request #337 from travis-ci/gc-update-android-sdk

Android SDK Updates and Bug Fixes