[WIP] aspect membership dropdown Backbone.js rework

* initial backbone port
* changed AspectMembershipsController#destroy to use aspect_membership_id
* included rudimentary jasmine specs
* more specs, updating the list elements after de-/selection
* update selected aspect count on button
* don't even try to render html in AspectMembershipsController
* more specs for button summary text
* adapt aspect management on contacts page and in the popup boxes

TODO
* more tests