OpenLP isn't playing well on HiDPI screens

Creating a public issue about the e-mail report and the forums comments (closes #1305).

Also see: https://forums.openlp.org/discussion/5768/remote-main-view-showing-black-screen https://forums.openlp.org/discussion/comment/15811#Comment_15811 https://forums.openlp.org/discussion/comment/15812#Comment_15812 https://forums.openlp.org/discussion/5970/very-strange-display-behavior#latest

The main question is OpenLP is not playing well with (at least) Windows DPI system. These are the main questions:

1. The screen resolution in the "Screens" settings tab is showing the real and expected screen resolution to the Qt system, but it isn't what user expects. Example: 1920x1080@125% scaling creates a 1534x836 screen resolution. Should the screen and positions inside OpenLP be relative to unscaled screen size? As it is now, it's confusing some users.
2. The Main View screenshot code seems to be not playing well with multiple HiDPI monitors (using non-scaled coordinates?). I could reproduce some of the Main View black screen symptoms with two 1920x1080@150% screens. If I place the display on the first screen, the Main View on Remote works. But if I place on second monitor, it stops working. It seems something on the OpenLP code is using non-scaled coordinates (needs more investigation).
3. There are some text that's not scaling well on higher DPI screens (like the Library labels). Is there something we can do about it?