Support basic Livechat features

[renatobecker-zz]

We need to extend the Apps/Engine, allowing to support basic Livechat features, such as:

Methods from Livechat library:

• Livechat.sendMessage(msgObj)
• Livechat.registerGuest(guestObj)
• Find Livechat Guests by a specific field(phone, id, token.. -> LivechatVisitors)
• Find (one) Livechat Room(s) by guest token(Rooms.findOpenByVisitorToken, findOpenByVisitorTokenAndDepartmentId);
• Livechat.transfer(room, guest, { roomId: rid, departmentId: department }))
• Livechat.closeRoom({ visitor, room, comment }));

Improve the interfaces, adding new specific Livechat fields:

IRoom:

• { v, ServedBy, closed, responseBy }

IMessage:

• { file, token, t }

In addition, we're facing an issue related to HTTP requests: We need to be able to pass the following props when sending an HTTP request:

• strictSSL
• rejectUnauthorized

[d-gubert]

We identified the need to access the Upload model through the engine, also

[renatobecker-zz]

We identified the need to access the Upload model through the engine, also

The same for Departments.. :P

[renatobecker-zz]

We need to support the livechat.closeRoom callback as well.