The IntanThread was occasionally looking for data after acquisition was disabled,
which would trigger the SourceNode to attempt to manually disable callbacks.
The only negative effect of this was that if the user was currently viewing
a different signal chain, it would switch back to the Intan chain unexpectedly.
This is no longer the case, as the SourceNode checks to see whether or not
it received a proper disable signal from the ProcessorGraph before notifying
the UI that data may have been dropped.

Generic Editors colors now match the type of processor.
The FilterViewport layout has been changed to a simple outline.

- Added a FilterViewportButton class to the UIComponent file, which shows/hides
the FilterViewport whenever it's clicked
- Thus, the DataViewport can now fill up almost the entire window

Tabs now work reasonably well when right-justified.

Border is now a square (except for upper-right corner).

There was a minor bug in the SourceNode code, which caused it to delay restarting
acquisition for about 1 second after acquisition was stopped. Now acquisition from
the Intan Board can be restarted almost immediately after it finishes.