Add support for the sectionbox and tcolorbox packages.

They will be used by the conference poster classes that will be supported in a minute.
Support for conference posters

The following poster classes are now supported:

* a0poster
* beamerposter
* sciposter
Merge remote-tracking branch 'github/build-bot-2.1.x' into bleeding-edge-2.1.x
2014.09.27-09.00