implementing the server-side selectize input

also added a new method shinysession$registerDataObj(), which was designed to be a general data retrieval method: we can store arbitrary data objects as "downloads", and return arbitrary http response based on the filter function; see renderDataTable() and updateSelectizeInput() for two examples
cosmetic changes (re-indent code)
closes #422: update the selectize options via updateSelectizeInput(options)
fix some JShint issues
Merge pull request #433 from yihui/selectize/server

server-side selectize input