Encode form values properly on output.  Fixes habari/habari#216
I don't know why Utils::htmlspecialchars() does half the crap it does.  It decodes stuff and then re-encodes, and even has a parameter to *couble*-encode things, which is just insane.  Why is this function even needed Utils?  Does the native PHP htmlspecialchars() not suffice?  Some reasoning behind these functions should be added to the PHPDoc, I think.