CMS ttbar 2D differentail distributions [WIP]
This PR contains the implementation of the CMS ttbar 2D differential distributions. It supersedes #183 in the following respects:
- the data sets have been renamed according to the new agreed layout; PRs # 4 in applgrids and # 38 in apfelcomb update the names consistently;
- the PR contains the implementation of the NNLO QCD K-factors; these K-factors should be replaced once A. Mitov's computation with a value of the top mass consistent with that used in the computation of the NLO applgrids will become available (hence why this PR is labelled [WIP]). Before merging, we also need to fix PR # 57 in buildmaster (that does not compile so far)