Make UI appearance universal

[shyamamrith]

• Currently the default UI only looks good on 1080p displays and is not scaleable; i.e. if you drag the corners, the contents does not move. The "high dpi" version is included, and is more scaleable, but also suffers from some distortions. Will need to look into how to use the 'Layouts' feature in Qt Designer to avoid this.
• Also, some computers render the UI in a different font, meaning that it can be difficult to read. This seems to be common on computers which use Chinese as the default display language. (Make new issue for this)

Might be useful: https://stackoverflow.com/questions/20464814/changing-dpi-scaling-size-of-display-make-qt-applications-font-size-get-rendere

[shyamamrith]

Scaleable UI mostly added in 0be9008, made default in f036260.
TODO: test on 4k monitor

[shyamamrith]

Fonts moved to dedicated issue #30

[shyamamrith]

Re-opening as the UI still does not display correctly on 4k monitors.

This has been tested on Windows; it is likely the inbuilt display scaling (which is usually very high for 4k resolution) is what causes this distortion. However, a lot of QGIS looks strange in this setup anyway - so may not be totally fixable.

It is worth checking another plugin's UI file for ideas on how to deal with this.