Cleanup of the mail text signature.

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