add client-side santized HTML capability
b/16896849
The semantics of the SANITIZED_HTML capability have narrowed. It now means
"Html email bodies for this account are assumed to be sanitized by the mail
server"
Consequently, accounts in Email no longer set this capability, but do set
the new capability permitting client-side sanitization of email bodies
Change-Id: Ie1343d8bedc2a17ab04e4df4b7c4ee14cfb01b64