htmlform: added ability to add optional classname to inputs
Merge commit '082f7e36405f01566b40147bb0c4d3ee03f7c050'

Conflicts:
	abstracts/input.php
Now allow field set to get a user defined class
Define clearValue on level of element. This avoids Fatal error (see #2)
enhanced file input to clear uploaded files on clearValue()
removed duplicate call to get classes in input
enhanced field set to include generic classes like 'required' and 'disabled'
fixed isEmpty definition
updated container so that clearValue clear values of child elements