Waveshaper

Here's the waveshaper pull request.

The plugin itself is working as it should, AFAICT. It has built-in linear interpolation of the graph, so shouldn't introduce any kind of quantization noise to the signal.

The functionality is simple, it's a unipolar waveshaper, so the graph is from 0 to 1, with input amplitude on one axis and output amplitude on another. Knobs for pre/post gain, buttons for reseting back to default/no-op and smoothing the curve.

Also improvements to graph widget: ability to draw straight lines by shift-clicking, fix of some old buggy behaviour: the widget no longer gets "sticky" if you go over the top edge. Also seems more responsive. mouseMoveEvent reimplemented in a better way, taking advantage of the new line drawing code. Smooth algorithm also improved, no longer shifts the graph to the right and is a bit closer to a gaussian function.

Also there are some commits that were in my fork when the branch was created, those are just some UI stuff.