Default only text string exists, via localized translation a wiki admin
can add his/her own (html) version.

Done:
Cleanup of the mail text signature.
The signature is deleted from the txt files and moved in to lang.php
Mailer.class.php updated to insert the signature

Fix:
- Cleaner text
- no more "-- "  "--" "---" "----" problems.
- mailwrap.html is not needed anymore an can be deleted (?)

Changed files in all languages:
lang.php
mailtext.txt
password.txt
registermail.txt
subscr_digest.txt
subscr_list.txt
subscr_single.txt
uploadmail.txt
pwconfirm.txt
showrev.txt

delete?:
mailwrap.html

This reverts commit 524df576.

Conflicts:
	inc/lang/bn/lang.php
	inc/lang/fr/lang.php

this has been done by a script and might not be 100% accurate

When loading plugins, $lang might not be initialized yet, so use a
hardcoded error message instead, especially as this error should only be
displayed for the admin (and then fixed). This also removes the
previously localized message, it might be re-added as part of the new
extension manager.