flatpak (build_manifest): some fixes needed after runtime update: - removed `--optimize=1` for lxml, as it is making the build fail - added build flag on x86_64 for Pillow (will need to be adapted if we build on other architectures) - added a module for Python 2.7.16, Python 2 not being included anymore in the runtime - DEFAULT_MANIFEST modules are put at the beginning of modules

[Desktop Entry]
Type=Application
Name=Cagou (SàT)
Comment=desktop/mobile frontend for Salut à Toi (XMPP)
Exec=sat_wrapper
Icon=org.salutatoi.Cagou
Categories=Network;InstantMessaging;Chat;FileTransfer;RemoteAccess;
Keywords=xmpp;chat;messaging;im;file;sharing;communication;jabber;social;network;decentralization;desktop;