docker: Libervia revision can now be specified: Using the `DOCKER_LIBERVIA_REV` environment variable, backend (and related repos) revision can now be specified. By default (variable empty or not set), the current `tip` version is used, and `dev` is used for tagging. If the variable is set, the revision will be used and used for tagging the image.

[Desktop Entry]
Type=Application
Name=Libervia TUI (Primitivus)
Comment=console frontend for Libervia (XMPP)
Exec=libervia-tui
Icon=org.libervia.LiberviaTUI
Categories=Network;InstantMessaging;Chat;FileTransfer;RemoteAccess;
Keywords=xmpp;chat;messaging;im;file;sharing;communication;jabber;social;network;decentralization;console;