flatpak: update files following names change + Python 3 update: - `build_manifest.py` has been fixed to work with recent SàT/Libervia - filenames/scripts have been udpated to reflect project name change - installation now uses `requirements.txt` when dev version is requested - there are now 3 types of commands wrapper: * `libervia_wrapper.py` uses `pb` bridge, starts backend before frontend, and stops it when frontend is stopped. It's used by `Libervia Desktop` (Cagou) * `libervia_wrapper-dbus.py` uses `dbus` bridge, starts backend before frontend, and stops it when frontend is stopped. It's used for `Libervia TUI` (Primitivus) * `libervia_wrapper-dbus.py` uses `dbus` bridge, starts backend if necessary and doesn't stop it (to avoid waiting for backend start next time). It's used by `Libervia CLI` (jp).

[Desktop Entry]
Type=Application
Name=Libervia Desktop (Cagou)
Comment=desktop/mobile frontend for Libervia (XMPP)
Exec=libervia-desktop_wrapper
Icon=org.libervia.LiberviaDesktop
Categories=Network;InstantMessaging;Chat;FileTransfer;RemoteAccess;
Keywords=xmpp;chat;messaging;im;file;sharing;communication;jabber;social;network;decentralization;desktop;