jsgui: Clear datatable so no duplicates when clicking between policies
Moves configuration of Backbone.View.prototype from router to view.js
jsgui: Adds generic modal and config key input views
jsgui: Attach new policies to entities

Basic implementation. Need to know the type of the policy.
Rework policy config editing

* Uses generic modal view rather than managing a modal itself
* Improved error display
* Shows default values in policy config table
* Adds Brooklyn.view.showModalWith(View) shortcut
jsgui: New policies are displayed immediately
This closes #126