android-sdk: update wrapper scripts.

- Clean up some of the user facing copy.
- Add examples of how to install the various tools required to use the sdk.
- Change the interpreter of wrapper scripts to /bin/bash
- Clean up the wrapper scripts.
- Change the default version of the Android Build Tools to 19.0.3.

Closes #27587.

Signed-off-by: Mike McQuaid <mike@mikemcquaid.com>