Fix UI font families to accept multiple fonts

[qyurila]

#30 found a bug and the underlying problem, but there had been no PR to fix this so I made one.

This PR makes UI font family config options to accept multiple fonts, by fixing the logic to wrap the value with "" only when it does not have a , (which implies the family of multiple fonts).

[knopp]

Shouldn't individual families (if multiple) still be escaped?

[j-f1]

You generally don’t need quotes in font-family, even if the name has multiple words (per MDN and my experience). As long as the font name doesn’t have numbers or other special characters it will be fine to leave it unquoted, and in those cases it’s easy enough for the user to put the quotes in manually.

[qyurila]

You generally don’t need quotes in font-family, even if the name has multiple words (per MDN and my experience).

Actually I didn't know that, I thought they should be quoted manually by user if there are multiple fonts given. Thanks for information!

Given that, would it be better if this if statement (and the below one) were removed?

[qyurila]

Got ready to be merged!