Significant improvements to audioplayer

[devicenull]

This is a fairly large change to audioplayer.php that adds the following features:

• Calls are retrieved via AJAX, and new calls are refreshed every 10s
• Audio playback will continue automatically when new calls are found
• Talk group selector was changed to use select2, which allows for searching the list of available call groups
• The file can now be installed anywhere - it does not require being in the "utils" directory (as long as you use absolute paths in config.json, and update audioplayer.php with the path to the config file)

I added a couple more Javascript libraries here... It took some effort to not rewrite this entire file to use a proper templating library and source control, but I figured keeping this as a single file was important

[rosecitytransit]

I actually have a "live" version that I made at https://github.com/rosecitytransit/trunk-recorder/tree/master/examples and discussed in #482

[robotastic]

Thanks @devicenull - I will merge this in.

@rosecitytransit - if you have some changes you want to make to the audio_player, that would be great. Could you open a PR for it? This is also a good reminder for me to look at the code in #482 and look into turning it into a plugin.