This commit checks on bootstrap what the currently configured theme
of the user is and loads the system tray icon in its corresponding
variation.
Unfortunately, MacOS doesn't seem to automatically swap out the icons
based on the system's theme, so we have to do it manually with two
different SVG files.
Another gotcha here is that, it doesn't seem to be possible to change
the system tray icon at runtime. When trying to reassign the `icon.source`
based on a newly selected theme, the icon disappears altogether.
The application also doesn't get notified when a user switches the theme
inside the operating system, requiring her to switch to the same theme
manually unless restarted.
Last but not least, using SVG files instead of PNG doesn't seem to solve
the problem that the icon is rendered blurry. I've looked in the docs
but there doesn't seem to be an option to have any influence on that...
Pascal Precht