Collada Exporter does not set a value for <authoring_tool>

[RichardTea]

Currently MakeHuman only sets a value for "author". It should also set a value for <authoring_tool/> specifying that the DAE was created using MakeHuman, the version used (version number and git commit hash) and the project URL.

This will make it much easier to resolve issues found when loading MakeHuman exports into 3rd party tools, as we can tell what made the problematic file.