Distraction-free mode

Why have a distraction-free mode?
When I'm writing a diary entry, I usually want to forget everything else and focus on what I'm writing. Distraction-free modes like the ones present in many writing apps like FocusWriter are great for that. They put text at the center of the user experience, making it much more enjoyable.

Possible implementation:
- While editing an entry, you could press F11 or a dedicated fullscreen button.
- The current UI would be replaced with a clean, full-screen background. The text of the current entry would be displayed with a slightly bigger font, as a single column with a comfortable width.
- Pressing Esc or F11 would switch back to the normal UI.

Possible customizable parameters:
- Background color.
- Text column width.
- Font size.
- Font type (less important).