portals: Users mass-deploy via CSV file

[cruzccl]

In 2e581a59 all exporters/importers where removed as they were not very useful (they required database ids).

This issue aims to add a basic user importer.

Given:

• Name (*)
• Lastname (*)
• Email
• Terminal
• TerminalModel
• TerminalPassword
• MAC address
• Extension
• Outgoing DDI

the importer should create:

• A new User.
• A new extension (used as screen extension for the user).
• A new terminal.

Important notes:

• The specified Extension must not exist. Otherwise, created User will have no extension assigned.
• The specified Terminal must not exist. Otherwise, created User will have no terminal assigned.
• The specified TerminalModel must exist, otherwise Generic terminal will be created.
• If TerminalPassword is omitted a random one will be used. If given, it must satisfy the password format as if it was introduced in the web portal (otherwise, a random one will be used).
• OutgoingDDI must exist. Otherwise, this field will be left unassigned.