* A new Start Linktest button is in the bottom right of the topology tab.

* When started, we create a new tab to display the linktest output
  (currently the unmodified output from Classic emulab linktest). The state
  of the experiment is change to linktest to prevent further action on the
  experiment, except of course for stop linktest.

* When linktest is running, there is a Stop Linktest button in the upper
  collapse panel. This will stop linktest in its tracks, but the tabs
  remain. When you kill a linktest tab while linktest is running, linktest
  continues running, you have to use the Stop button.

* I have added a small help document to the templates directory that the
  user is shown when they click on the ? mark in the linktest modal.
  Written in markdown format, it is a culling of text from the Emulab wiki
  linktest page.

Caveats:

* Because of polling, there is a short (5-15 seconds) delay before the
  experiment is returned to the ready state. Not much to do about this in a
  polling world. Wouldn't callbacks be nice?

* Linktest can be used on a multisite topology, although cross site links
  cannot be tested at this point. Links/Lans that are contained entirely to
  one site or the other are testable though. We build a new tab for each
  site to spew the linktest output.