Progress dialog when loading waveforms gives confusing/inaccurate results w/ mixed signal captures

[azonenberg]

Right now, all channels/waveforms contribute equally to the displayed progress.

This is commonly not accurate: digital captures have less bytes per sample and are often captured at lower sample rate than analog ones. A better option would be to scale progress by the size of the waveform .bin file (easy to stat before actually doing the load) so that progress more accurately reflects the percentage of bytes read. This is likely a much better proxy for percentage of load time than percentage of channels loaded.