Add scc travis-merge to the Travis before_install step

This PR integrates the scc features added in openmicroscopy/snoopycrimecop#77, openmicroscopy/snoopycrimecop#79 and openmicroscopy/snoopycrimecop#81 into the openmicroscopy Travis build.

Before Travis builds the server and runs `test-compile`, `scc travis-merge` should be called which performs the following actions:
- bumps the submodules to the HEAD of `origin/$branch`
- merges all the PRs specified by ``--depends-on #prnumber`` or ``--depends-on repo/name#prnumber`` in the comments of the PR