* Set max width for channel labels to 12 (wide) resp 8 (narrow)
* "Ellipside" channel label if it is too wide.
* Add tooltip with full channel name to label if it is too wide
* Make font size of channel label smaller if set to narrow
* Move channel label and wide/narrow related code into
`Channel` base class, so it works th same for input and output
channels.
* Use `super()` in `Channel` sub-classes where appropriate
* Dont use class attributes in `Channel` class for per-instance
data.
Signed-off-by: Christopher Arndt <chris@chrisarndt.de>