Improve associated Android Git selection and add credential

[Cervator]

Tweaks at how branching is handled for the Android repo

• master in this repo will build master in https://github.com/MovingBlocks/DestSolAndroid
• develop likewise will build develop
• Any topic branch in this repo that begins with android/ will build the corresponding branch from the Android repo
• Any other topic branch will default to develop in the Android repo

Also adds a Git credential just for API limits and what not

Tested with some Nanoware branches: https://jenkins.terasology.io/teraorg/job/Nanoware/job/DestinationSol/ - validated that the right repos were getting cloned via logging.

[Cervator]

(checks are expected to fail, this PR is what'll fix them but after merge)