fix: the font switcher now remembers your previous font

[pajlada]

Fixes #2112

I would appreciate someone other than me testing this out to make sure I've covered everything

You should be able to:

• select one of the predefined fonts and the chat fonts should update
• select "choose" which opens a font dialog & select a custom font
• select "choose" which opens a font dialog & select cancel (which should revert back to your previously chosen font)

[pajlada]

j