Add the ability to send a message to several groups
Description of the new feature
At the moment, it's possible to send one message exactly to the one contact's group. It's possible to select several groups in the roster, but right-click over them doesn't show anything. It would be nice to implement the ability to send a message to the selected groups. Especially we're loved such possibility when we're used Psi+. Such feature is very usefull imo, atleast inside our organization where we are using Gajim everyday. For example: one of ours employees needs to make announcement between all or several departments, at the same time the departments - groups in the roster, to make the annoucement beetwen several group, employee needs to select the wanted groups one by one and repeat the same operation.