255 stickies

Fix #255, and more specifically the following issues:
- deprecated methods in notice model, stickies and notices views
- modal windows realized by Thickbox;
- loading gif for modal windows;
- ajax forms for creating new stickies (stickies/create.js.erb);
- auto-check checkboxes for locations in the advanced options (locationcheckboxes.js)

The following issues are NOT yet fixed:
- enable JS in the modal window

The reason that JS is not working in the modal window is that all events are bound on document ready, so since thickbox adds new `#TB_ajaxContent` dynamically to the page, none of the elements in the rendered modal window is bound to the correct event handlers.

We are thinking about using bootstrap for the modal windows, which may make the situation easier to fix. But right now this is a working version for creating new stickies.

This is built on top of both #235 and #254. I need the former so that I can get to report show page which has the links to post stickies; I need the latter because I added thinkbox.js into the rearranged vendor directory.
[See the compare between HEAD of this branch and the commit that merged #235 and #254](https://github.com/YaleSTC/shifts/compare/d945436666e99221260fe24d76cc866256309763...255_stickies?w=1)