Add ability to assign Client records to Users

Similar to how Leads can be assigned to Users, Clients can now be assigned to Users.

Assignment can be performed via the Admin tab in the Client record or in bulk via the Manager Report.

Filters and columns have been added throughout DMA Reports including: All Clients, Client Balances, Search, Client Docs, Client Messages.

There is a new Assignment Report that displays the number of assignments per User by Client Phase.

There is a new DocumentTemplate variable called $UserBackend that contains the information of this user.

Task functionality remains unchanged for the DMA.