Problem:
- There's not yet a way to get the parameters for each channel
after it's clicked

The control panel now holds an "AudioEditor" to adjust volume
and open a window to alter device settings. Audio output is definitely
working, but different buffer sizes make it sound really weird. The
same problem is present in the Juce demo app, however, so I don't
think it's a problem inherent in the GUI.

But they won't do anything useful until the ProcessorGraph is updated

The EditorViewport now contains buttons to scroll through multiple tabs,
or scroll across long signal chains. Now, there can be infinitely
many signal chains of infinite length (if you have a lot of time
on your hands).

Functions for managing the signal chain are no longer handled by
the EditorViewport, but by the SignalChainManager

Three important changes:
- The FilterList is now the ProcessorList
- The FilterViewport is now the EditorViewport
- Any classes that need to access important UI objects have become subclasses
  of the "AccessClass". Such objects automatically obtain pointers from
  the UIComponent and register the MessageCenter as an ActionListener. This
  will make it much easier to allocate pointers to objects.

Previously, if you placed a sink in front of a source, it would lead to
a never-ending "while" loop. By removing two lines (254-255), this problem
was solved.

In combination with an EventNode, a WiFiOutput node is able to send a
simple message to a hard-coded address via UDP. This is the first sink that
actually emits an output. It's obviously over-simplified, but as a
proof-of-concept, it seems to be working well.

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.

Changes to the DataThread, SourceNode, and UIComponent classes allow data
threads to disable callbacks if they are no longer receiving input. So
far this has only been tested with the Intan Board, but it works really well.
Unplugging the board in the middle of acquisition allows the thread to exit,
and callbacks to be disabled, without any seg faults.

DataThreads (e.g. IntanThread, FileReaderThread, FPGAThread) are now created at
the same time as the source node, rather than at the start of data acquisition.
New methods for starting/stopping individual threads are required, although
only the appropriate methods for the IntanThread have been written.

Another important change is that the SourceNode now periodically checks for
an appropriate input source every few seconds while acquisition is not in
progress. It's the responsibility of the individual DataThreads to notify
the SourceNode if their input has disappears. In the case of the IntanThread,
this involves attempting to change the baud rate. If an error code returns,
it informs the SourceNode that the input is missing. This, in turn, informs
the FilterViewport that the source is no longer enabled, thus deactivating
that particular signal chain.