InputWidget: DOM property is 'readOnly', not 'readonly'

This works because of jQuery propFix (which maps a set of common
mistakes, but should not be relied on). The HTML attribute (only
used to set the elements initial state) is "readonly", but the
live node property is "readOnly".

Change-Id: If0ef07f0729b90ae3cfb156e3a526d10708b8c75
Merge "InputWidget: DOM property is 'readOnly', not 'readonly'"