Set contentEditable using jQuery#prop

Also always use strings 'true'/'false' for the value, because
it is a string property (spellcheck, however, is a boolean)
and always use a capital second 'E' in the name.

Change-Id: Ia4e1f9edfd8f236fe81df190e6a68729d7b52243
Merge "Set contentEditable using jQuery#prop"