LFP redraws are now incremental
LFP traces are now only drawn in the space since the last buffer update, this reduced cpu load.
Reverted back to the linedraw method because speed is not an issue any more with this fix.
Currently not issuing full redraws when a user uses the scrollbar, only for clicks and mouse wheel messages.
Increased visualizer callback frequency
20ms work very smoothly on a 1.2GHz core 2 duo laptop, so it's probably a safe value.