Settings now open inside the main window

Also removed unnecessary margins from layouts
Update Finnish translation
Fix signal used to listen for changes in preferred languages

Fixes UI update issues when they were (un)checked using keyboard

Also clean up the ListWidgetItem construction to fix a new bug
that appeared with this signal change
Minor layout change in settings
Minor cleanup
Add keyboard shortcuts for opening and closing settings

Get rid of our copy of the configure icon in the process.
Now the "configure" icon of the current icon theme is used instead.
Update Finnish translation
Leaner CMakeLists.txt files