Possibly do something about untuitive features of multiple tabs

[lmcmicu]

Now that we have changed the view-rebuild process to use multiple tabs (see #65), the following situation might occur:

1. User clicks on a view that is out of date, which DROID opens in another tab ("tab 2"), and the user confirms that she wants to rebuild it.
2. While the view is rebuilding, the user switches to the original tab and for whatever reason decides to launch another process, which kills the view rebuild before launching.

The result is that "tab 2" no longer shows the process that is rebuilding the view in the console, but the new process kicked off in step 2.

Right now we are displaying a warning banner in the first tab after the process gets killed to let the user know that they should close the second tab. This avoids some confusion but it is less than ideal as it clutters up the interface, oftentimes unnecessarily.