Some UI rework

[mincequi]

Hey there,

as I am working with this App extensively, I would like to come up with some UI improvements:

1. Remove the Excitation Generate button and do not write excitation file to disk. Instead, generate Excitation in-memory, when pressing "Start recording". This is easily fast enough.
2. Integrate the Plot view into the main ui, so that there are no extra windows floating around.
3. To save space for 2., I would like to create some top-level taps like "Settings", "Measure", instead of having that all on one single page.
4. Reduce the Measurement sets table to a single column (Description) to save space for plot integration. The details could be shown elsewhere on the ui. I do not believe, someone is interested in "Uses excitation" and "Max. level" in advance of selecting a measurement.
5. Add Material icons: https://github.com/sthlm58/QtMaterialDesignIcons
6. Add possibility to load microphone calibration files (in "Settings" tab).

I would like this project to catch up with https://www.roomeqwizard.com and do a general modernisation.

What are your thoughts? I would continuously provide PRs for that rework.

P.S.: I know, that the PortAudio integration is holding us back. However, things should improve, when the platform-specific issues are done.