swarm: add context menu for members

In the members list, a right click allow the user to access some
actions such as:

+ Perform a video or audio call with a member
+ Open a 1:1 conversation with this member
+ Block this contact
+ If allowed, kick a member from the conversation

In the future, other actions can be added, such as promote a user
to administrator.

GitLab: #340
Change-Id: I3824ad4efa8faf89479e99c93b98d3dd9781582d