Incorrect operation in mono

[anthonyalfimov]

Plugin is not properly optimised for operation in mono. Behavioural issues encountered so far:

• Meters are not redrawing automatically (only when forced by some other event)
• There are two meters - should be just one
• Chorus might not be working at all (checked only on laptop speakers, not sure)

Code issues:

• DSP modules for both channels are always allocated, even though in mono we only need just one of each.

[anthonyalfimov]

Fixed all of the above.

TODO:

• [x] Disable "Width" control in mono mode