Add a configure switch for disabling UI component

[hnyman]

In embedded device context the UI component may be unnecessary.
Please provide a configure switch to disable UI compilation.

(I disabled it manually by reverting bf92971 )

[veruu]

I'm away next week, but I'll take a look at both your issues as soon as I have time. Thanks for bringing it up!

[nhorman]

fixed in commit fd12d96

[szepeviktor]

fd12d96