Blender Git Loki

Fix T46189, draw style for waveforms occludes sequence strip text.

Used old (2.49 era) filled style for drawing here, with white color and
alpha blending.
Also changed drawing to do linear interpolation between samples instead
of ugly square wave in high zoom.
This could be improved upon, with real waveform drawing in higher zoom
levels, but I'll leave this for later since it may need some hacking on
audaspace level.