add a special source file only for stable

With source-master.yml, autoproj would bail out if trying to
checkout master-only packages (as their version control definitions
did not get loaded). This commit moves the master into source.yml
(as "default") and the stable into an extra file
move base/orogen/interfaces to stable, it is required by the rock1408 branches

Janosch forcefully pushed the relevant changes. Great to move
never-released deprecated code into a release