Changed password handling + Forgotten password functions

- Better password handling (PHPass instead of decryptable password hashes)
- Passwords will have to get "migrated" using the "installer"
- Removal of bug "send forgotten password request for other users" (you will get an email to confirm first - else others could spam requests for your email-account)

Attention:
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To make "confirm password reset"-pages etc work, you have to create the pages in your theme - and write templates for them. That is why I did not include them. IF REALLY NEEDED: I could add some for one of the default themes.
But... it is nothing more than the needed forms (see forms.php) and response pages.