Create multiple multiview outputs per production

[malmen237]

What does this do?

When setting up a production this allows for adding multiple multiviews to each production, for the possibility of having multiviews with different setups.

Layout

Added buttons to add and remove additional multiviewers, when only one multiview remains the button is removed.

When production is running, all multiviewers can be located in the control window to the right.

An easier way to start all multiviewers at once is to install mpv-player ("brew install mpv" on mac) and then run all srt-links in the command-line "mpv srt://0.0.0.0:1234 & mpv srt://0.0.0.0:2345 & mpv srt://0.0.0.0:3456"

[malmen237]

Summary of comments from old PR:

• I'm guessing that multiple multiviews cannot use the same port. What happens now if you set the same port number on more than one?
• Why should we restrict removal so that at least one multiview exists? Shouldn't it be possible to remove them all? Not possible atm, if desirable needs a larger restructure where multiview is not a mandatory-value.
• Each run through of array does not connect to right id, therefor only first multiview works atm.
• Add copy link to all multiviews.
• Removing source from running production is causing error.
• We probably want to modify the production settings model to say multiviews instead of multiview that should make it easier to support both the old and new data model as well.
• Add clearer distinction between runtime and setup code. I've added where I've updated the code, but a larger work would need to be done for thinks to be made more clear.

[Saelmala]

Overall LGTM, just left a couple minor comments about code clean up