Improve Windows installation and update process

[Xayton]

There are multiple improvements that can be made to the Agent on Windows (which is the most used OS according to our download statistics):

• Investigate if it's possible to install the Agent on Windows without needed administrative rights. This might need changes in the setup process. This could help a lot our customers that do not have admin rights on their computers.
• Investigate reports of the Agent restarting, after an update request from the front-end, but not updating and not restarting afterwards.
• Ensure the setup, on Windows, can be run in "no gui" or "silent" mode. This is helpful when installing the Agent automatically, for example for a set of computers in a Windows domain. Also document how this works and how people can use it.

Other things to check, while working on the install flow:

• Make sure that the installer is usable on HiDPI displays
• Make sure the installer is usable when using the dark theme (on 3 operating systems). We had reports that some text does not get the correct color and is barely visible in dark mode.

[umbynos]

Which step of the installer requires admin rights? By searching in the installer configuration I see there are multiple occurrences of <runAsAdmin>0</runAsAdmin>, probably the default is 1 and we forgot to set it to 0 in some step.