The Intan recording module allows users to route two channels to the
audio jack on the acquisition board. Up to this point, selecting channel
1 in the params tab would output software channel 2. In addition,
channel 1 is inaccessible.

This stems from a mismatch between the one-based indexing used by Open
Ephys GUI and the zero-based indexing that the Intan ecosystem uses.

* Added docs for the class. Override only buttonEvent (as for other non-visual editors)
* Started fixing other editors, a lot of redundant code can be removed.
* See comments in VisualEditor.cpp