To prepare for translation support, this makes all of the widgets
cognizant of the language change event that occurs whenever
installTranslator() is called and automatically retranslates their text
where necessary.

This is important as calling the backing UI's retranslateUi() is often
not enough, particularly in cases where we add our own strings that
aren't controlled by it. In that case we need to manually refresh the
strings ourselves.

Calling tr() from a file-scope array isn't advisable, since it can be
executed before the Qt libraries are even fully initialized, which can
lead to crashes.

Instead, the translatable strings should be annotated, and the tr()
function should be called at the string's usage site.

Greatly simplifies the current input UI, while still allowing power users to tweak advanced settings. Adds 'input profiles', which are easy autoconfigurations to make getting started easy and fast. Also has a custom option which brings up the current, full UI.