Add some help / informational text areas

This is a WIP, but I'm opening a Pull Request so the changes can be discussed more easily. *Please do not merge this yet.*

I just added some rudimentary labels for help / info texts in the key overview and accounts tab. They are ugly and have no sensible content, but they should give you an idea on what I am aiming to do (see Issue #22 for more information on the "why" and "why now").

Please feel free to comment, or submit your changes (push to feature/help-text-areas).