The SpikeDetector now uses SpikeObjects to pass spike messages,
rather than the GenericProcessor "addEvent" code, as previously.
This makes it easier to distribute spikes to multi-channel electrode
displays, such as StereotrodePlot and TetrodePlot. However, there's
still a problem with setting the axes. "Real" spikes have an issue
with constantly changing the axes, whereas simulated spikes do not.

Through the SpikeDetector Editor, it's now possible to change the channel
mapping for each electrode and adjust thresholds. It's not yet possible
to inactivate particular electrodes or change parameters over multiple
electrodes at once; these will both be necessary functions in the future.

Now, when the user clicks on a tab in the DataViewport, the corresponding Editor becomes
active. Likewise, when the user selects an Editor with a Visualizer, the corresponding
tab becomes active in the DataViewport.

Channel selection now takes place within a slick new interface. It's not
yet tied to actually changing parameters, but things should be much simpler
code-wise, as well as visually.

Added method for creating parameter editors, which can be overridden by subclasses of the GenericEditor