Introduce vhosts for allowing isolated environments under same installation

[evlach]

Summary

The idea is inspired by rabbitmq. In short:

• a vhost is an isolated environment with its machines and streams
• A user can be associated to one or more vhosts
• A user can switch between his vhosts after login
• The admin can create/delete vhosts and give access to users for specific vhosts

inspiring screen from rabbitmq

Motivation

• This will allow more project / scope specific virtual installation and make things clearer for small teams to work.
• On a cloud installation this will be a very important feature
• This is an easy alternative to complex user/resource management

Additional context

Implementation should not be difficult. Foreseen changes:

• add vhost in user model
• add vhosts maybe in config global collections and allow admin to add/delete
• allow creation / connection to db collections based on vhost as prefix
• add vhost in MQTT topic maybe under protocol version in have a kind of mosquitto vhost
• add vhost selection ui widget