- removed non-working "2nd file handle" hack for temp file removal
- added workaround for ENGINE-729 bug
- removed non-working IMAP specific code copied from TB's RemoveDraft().

- removed storeProtectedOptions.
- renamed getPassiveMode to isPassiveMode for consistency.
- renamed unprotectedSubjects to protectSubjects.
- reformatted options.xul and aligned strings with Outlook.

The implementation was highly defective:
* It only added the disclaimer to the text part, not the HTML, so it wouldn't have been visible in HTML messages anyway.
* Even for plain text messages, it would have potentially been placed after the signature, so in some clients it would have been dimmed.
* Putting it into a HTML message really required HTML parsing unless we wanted to add it after the HTML body.
* It ran yet another rating adapter call to figure out whether the message would be encrypted.

If not disabled, we should always run the message through the engine to append the key.

First step of listing all identities on the options page.
Main changes are in rev. 397efff2cb3a. Account options and identity options still need to be separated.

- renamed options.xul -> options.xhtml
- Moved cancel/save buttons from first tab to all tabs
- Use identities instead of accounts for preferences using identity.key
as an id.
- update privacy bar when changing identity
- getIdentities() now returns an array instead of an enumerable
- check if the message should be encrypted using identity