Fixing handling of StreamerId in the initial config settings.

[mcottontensor]

Relevant components:

• Signalling server
• Frontend library
• Frontend UI library
• Matchmaker
• Platform scripts
• SFU

Problem statement:

As described in #436 setting the StreamerId in the initial config does not work. This is because if we try to set an option selection that isn't already in the list the selection is ignored, and additionally when we get the streamer list, this option list is thrown out and reset with the streamer ids.

Solution

• The setOptionSettingValue now adds the selected value if it doesn't already exist in the list. Without this the selection does not happen.
• handleStreamerListMessage now checks the existing selection and uses it as the default wantedStreamerId. It also now correctly checks whether we're allowing URL params before checking them for the StreamerId.

Fixes #436

Documentation

Test Plan and Compatibility

[lukehb]

lgtm