js: new algorithm to update main navbar changes

…plus other minor things.
Details:
- handlePlexConnectNavbar.js: extracted from utils.js, new function
reloadNavbar() to handle/double check onVolatileReload (updates main
navbar in place, no need to exit nor double-navbar quirks)
- settings.js: removed atv extensions (rely on utils.js), “spinner”
during sign out, support new navbar handling
- trailers.js: extracted from utils.js
- updateXML.js: removed atv extensions (rely on utils.js)
- various .xml: adapt scripts in use
- PlexConnect.xml: define volatile, rely on handlePlexConnectNavbar.js
to figure out what to do…