Contact list and aliases

[thesheepcat]

Currently, all peers who are communicating with user, are identified by their address; if peers number grows, user will struggle on remembering "who is who".
We need to add a contact list where user manually assign a username/alias to each address.

UI have to be adapted to let user to:

• Open the contact list
• Create new contacts, assigning existing or new addresses;
• Update and delete contacts;
• See username/alias on both sidepanel (ChatBox component) and mainwindow (ContentHeader component).

It's a good use case to start implementing a dymanic navigation sidebar which opens when headerButton il clicked.