Jchansen/add image request form

1. Added the Request Image form, found by going into an Instances details page.  The form doesn't submit yet - that will be a future pull request.  

2. Pulled in Chosen (a jQuery plugin for select and multi-select forms) and styled it like Bootstrap.  For that I pulled in the official sass port of Bootstrap (as a bower package), because variables in it were required by bootstrap-chosen (the sass library that styles Chosen components like Bootstrap).