Vendor has a picture atrribute, and was displayed in one form of the
splashpage, but it wasn't exposed in the vendor editing form, nor was it
included in the "map view" on the splash page.
Additionally, the map popup was rendered inline.
This commit:
* Adds a from input for editing Venue#picture, consistent with other
form elements
* Displays the picture on the splash page in either style (map or
static)
* Moves the splash page map popup from inline HTML to it's own partial
* Consistent route/model/controller/view layout
* Get rid of unused photos, speakers, dietchoices, social_events controllers
* Drop unused :public from Rooms and :description from CallForPapers
