Allow maxlength attribute on HTMLSelectAndOtherField

Allow maxlength attribute on HTMLSelectAndOtherField

A reason on a SelectAndOtherField can have two parts, one of the scroll
down box and a free text field. The free text field is actually
unlimited.
This patch allows the maxlength on that field. To respect the concat of
the two parts, also javascript code is added, which adds a dynamic
maxlength to respect also the text from the scroll down box.

The HTMLSelectAndOtherField is only used on Special:Block,
where the maxlength attribute is now set to 255 (length of the database
field ipb_reason).

Change-Id: I5c164b41ab047e7ecf9d92db6eddcc980e2db048