Drawing isochronal lines

[drsewilliams]

Rainbow colour scales have several limitations. It would be helpful to add the functionality to draw isochronal activation lines. This should probably be created as a standalone function.

Functions such as drawMap.m could then have an additional parameter-value pair such as 'isochronal' {'false'} | true. If set to true, after drawing the map the isochronal function could be called to add the isochronal lines.

Possible header:

drawIsochronalLines(userdata, type, options)

userdata - userdata structure
type - 'uni' | 'bip' | 'lat' | 'cv'
options - a structure describing the lines, for example options.min, options.max, options.interval