Waveform: Graphical improvements

[matthewh806]

The creation of the zoom functionality in the waveform has increased the need for some kind of "grid" like visual indicators. Otherwise it's quite easy to get lost in the file.

• [x] Add a line through 0 in both channels
• [x] Add a separator between the two channels?
• [x] Label samples at set increments, respecting change in zoom levels (does this imply ruler creation...?)

This should be general enough to put in a wrapper class with the bass waveform. With functionality to show / hide these elements as they could be distracting

This should be enough for now. In future we can think about adding grid lines, different timecodes etc

[matthewh806]

Yes it did imply ruler creation!