Allow UI layout and configuration to be permalinkable

[mgrauer]

No description provided.

[danlamanna]

A couple of things to consider:

• Currently, Girder's Backbone routing is still enabled - going to http://some-minerva-url#plugins will yield Girder's plugin listing.
• What is the maximum length of permalinks?
  If we (and any plugins) want to store attributes in the URL we should probably keep this mind. I don't think it will be a huge deal, though keep in mind certain configurations of the Taxi app have nearly 500 characters.

[jeffbaumes]

@manthey has another solution that saves the app state to MongoDB and puts the ID for that state in the URL instead of enumerating all options in the URL directly. He has used this in another XDATA application. This may be a better general solution to this problem.