Check only for active records when performing a duplicate check for mailboxes / aliases / forwarders

Added a missing language string in server config form.

Updated version number to 3.0.1.4 and changed sort order to domain name in the mailbox, alias and forward forms.

Updated jailkit instalation procedures to install jailkit as debian package. Because it´s better to remove and update. And because jailkit is debianized.
Install debian package is better then pure source.

Improved client and reseller limit checks

Fixed: FS#810 - FTP - If username is left blank and client clicks options a clientname_ blank username is created.

Fixed: FS#787 - A sub-client can see all the clients on the system in the client drop down list 

Fixed FS#775 - Client can choose the servers for it's client 

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