set buffer font in input bar

[benharri]

not sure if this is the desired behavior, but the clash between buffer and input bar fonts was bugging me.

if it's useful, great; otherwise i'll just keep using it for myself.

reopened from #412 against master instead of light-theme

[oakkitten]

for this to be merged:

1. it needs to respond to user's changing font via preferences
2. it needs to be an option
3. most importantly, we need a bit more users who want this feature 😬

(p.s. i'll merge this as is for 💲💯)

[benharri]

This just sets the input bar to use the same font configured for the buffer. It respects the current setting for the buffer font.