Live Stream properties of "Title" and "Description" should come from a template rather than code

[goodtune]

Currently the title and description properties that are sent to YouTube come from statically defined template in the Python code of edit_match view. This is obviously not very flexible, so we should move towards a system that is template based.

Extract these values from the code and make them be sourced from standard templates, this will allow us to override them on a per-site basis.

Further, they should be easily overloaded by competition, season, division, stage. There should also be sensible template blocks to make partial overloading simpler.

Pick a sensible set of values for the context, but it must be able to continue resolving what is already defined.