Averaging, resistance/reactive chart and small screen improvements

This release brings averaging as a new feature: Press "Sweep settings" to select between running a single sweep (of optionally multiple segments), a continuous (live) sweeping of the range, or to average several sweeps from the NanoVNA. You can configure how many averages to make, and optionally, how many of the sample points to discard, based on which deviate the most from the rest, and are least likely to contribute signal.

Also added is a new Resistance/Reactance chart, which shows both the R and X component of R+jX. This brings the challenge of showing two traces for the same data - added is therefore the option of picking a secondary colour for sweeps under "Display settings".

There are further improvements to UI sizing, meaning the interface now fits - tightly - on a 1366x768 screen, at least on Windows.

A few quality of live improvements made it in: Press escape in any of the pop out windows to close them instantly. The calibration window now shows more clearly when the source of calibration data is loading from a file, and also the number of points loaded. A few crash bugs were fixed.

I look forward to hearing feedback from all of you!