Support for per-board urls.

- Added loadQueuedBoard: Sets currentBoard to queued board id. Its context is subscribed to boards so that it can load a board when the boards are ready.
- routing.js: Takes the urlId and sets urlIdToLoadOnRender, which will later be used by loadQueuedBoard.
- Added backbone for routing.
- Created boardURLId() in models, used in createBoard and copyBoard to set urlId on the board.
- Template.boardList click even now fixes the url to match the selected board.
- URLToBoard is now shown in board metadata.
Improved spacing in add/copy board forms a little bit.
Got rid of select-disabling stuff.
Added http:// to board URL. Added some highlighting to board URL. Consolidated visibility-label and writability-label into metadataLabel.
Desaturated URL highlight slightly.
Pre-fill name field in copy board form.
Fixed new board loading, post-board creation.
Maintain correct URL after copying or creating a new board. Factored session setting and history maintenance code from boardList.click out into updateBoard.
Pulled panToCenterOnRect out of lockZoomToDefaultCenterPanAtDataCoords and used it after successfully adding items and boxes in boxadder.js.
Replace *all* spaces in the urlId with -.
Got rid of some log messages.
Removed redundant error divs.