Automate OBS more

[adriweb]

The _service rules can apparently be used to automatically get the latest version from git.
After that, extract the latest libpng-apng archive into the gui/qt/capture folder, then start building as before.

[adriweb]

This isn't so much needed, it's easy enough to just update all files in the .tar.xz (just don't forget to add the libpng-apng stuff) and update the metadata files (see da946dd)

Also, test project (CEmu-dev) on obs before submitting on the real one.