Added a missing license header
More organization for the trace input form.
I rearranged the state management of the form to use Bacon.js more centrally, and added a 'disabled' state to the OK button when the form is invalid.
Also a couple of assorted small fixes like moving common.js to the common folder, and adding the missing 'header-push' div to the traces page.
Removed the old upload form from the TraceSwitcher.
Also added a separate button for "Import trace", next to the "New Trace" button.