Move backend to its own namespace.
Move Signaler to its own file.
Move backend's components to its own file.
Merge remote-tracking branch 'refs/remotes/ivan/feature/split-backend-components' into develop
Pin Riseup
Merge remote-tracking branch 'chiiph/feature/pin_riseup' into develop
wait for deferred decryption to finish before going on
ensure clean termination
explicitely defer encryption
invoke mainwindow.quit only from parent pid

because the fork happens after the registration of the signal handler,
all children processes were inheriting the handler (and being passed a
reference to the mainwindow object, ugh...)