{Reviewer: Felix} Frontend chanes for a UI to configure application servers

This is all the JS and HTML to provide an Ellis UI to configure application servers - it ads a fourth tab to the Configure dialog, with a list of checkboxes labelled OpenSIPS, CFS, etc.

Once I have the backend API working as well, I'll update a couple of lines of code to put/get from that appropriately, but that will be a very minor change.

I found it much simpler to define a JSON file to map AS names to XML blobs, rather than the extended XML format that was proposed in the email trail. Do you see any problem with that?