- Fixed diag to work with new SFML version.

- Fixed diag to work with new SFML version.
- Added thread local contextual information which currently include channel and layer where applicable (used by diag).
- Created graph_sink abstraction, separating diag backend from diag API.
- Bundled liberation fonts for use with SFML font rendering.
- In addition to ordinary diag OSD window backend an OSC backend has also been implemented:
  /diag/[graph_id]/text <string> for the name of the graph
  /diag/[graph_id]/color/[value-name] <int> for the 32-bit rgba value of the color for the tag or value with the a given name.
  /diag/[graph_id]/context/channel <int> for the channel that the graph concerns (if any)
  /diag/[graph_id]/context/layer <int> for the layer that the graph concerns (if any)
  /diag/[graph_id]/value/[value-name] <float> for the value generally within 0.0 <= n <= 1.0
  /diag/[graph_id]/tag/[value-name] only sent when an "event" happens, like a dropped frame or similar. Generally no values are sent for value-names dedicated for tagging.