[16.0] [ADD] helpdesk_mgmt_ticket_follower: New module

[BernatObrador]

Portal Ticket Follower

This module adds the posibilty to add followers to a helpdesk ticket from the helpdesk form at the website portal.

Usage

To make it work you just need to add the emails of the wanted followers to the Add Followers input splitted by comas.

cc https://github.com/APSL 158607

@miquelalzanillas @lbarry-apsl @peluko00 @javierobcn please review