Fixed: FS#943 - ErrorCreating Email Mailbox - possibility co create mailbox name with CAPITALletters 

- Fixed bug FS#410 (http://bugtracker.ispconfig.org/index.php?do=details&task_id=410&project=3&order=tasktype&sort=asc).

- Improved installer and updater for multiserver mode. Modules and plugins were only configured if the selected service is available on the server.

- Update server.ini during install
- Changed default vmail directory form /home/vmail to /var/vmail

The mail box quota wasn't being run on mailbox creation. I had previously only fixed it when the mailbox is changed.

They both work fine now.

This is suppose to fix the bug where maildrop and maildirmake doesn't rebuild the /maildirsize file. 

- Fixed bug with maildir creation in mail plugin.

Updated the Debian installation instructions.

Updated ToDo item list.

Moved server modules and plugins to new directory and updated the installer to create the symlinks for the modules and plugins from *-available to *-enabled directory.
Fixed a typo in mailfilter template.

Added a server module for clients and a mail plugin.