Support new dynamic list of DASH IF test vectors in reference player

[siropeich]

Issue #2276

Notes

• I had to remove the max-height limit (and overflow) in the stream dropdown, as it doesn't work on entries with children. This would require some hacking in the bootstrap dropdown or using a different component, so I decided to skip it.
• Point 3 (only load in the remote sources if the user selects "DASH Industry Forum test vectors") wouldn't work for mobile. Remote sources are asynchronously loaded once local sources are ready, so user experience should not be affected.