Add source module to mumo

The source module is inspired by the bf2 module and is supposed to allow on-the-fly context/identity based player management for source engine based games. Currently supported games are TF2, DOD:S, CStrike:Source and HL2DM.

This commit adds the basic structure with unit tests for many of the components. For now only dynamic channel creation and player movement is implemented.

Left todo are dynamic ACL/Group management, unused channel deletion, server channel re-use and, most importantly, actual testing beyond the small unit test coverage.
Add a README
Add capability to delete unused channels to source plugin