Add "New Public Master" option to MasterChooser.

This PR adds the option of creating a New Public Master in the
MasterChooser. In order to do this, the startMaster call was moved to an
AsyncTask to prevent network activity in the UI thread.

The PR also modifies the layout of the master chooser, to accommodate
for the new option in a somewhat nicer way.
Add deprecated version of startMaster.

To prevent breaking existing applications a deprecated version of
startMaster with no arguments is added. This method only creates private
masters, which was the original behaviour.
Simplify MasterChooser interface.

Now the MasterChooser UI only shows the options relevant to connecting
to a robot by default. A checkbox is added to show "advanced options"
which uncovers the new master and new private master options.

A checkbox is used instead of an on/off switch because the switch needs
a higher API level than the currently used.
Merge pull request #169 from rosjava/new-public-master

New public master option to master chooser