implement listen method for DBus
listen(number<s>) -> <>::
add \-\-number option to daemon subcommand
- permits starting daemon in anonymous mode with zero or more numbers
- numbers may be added to daemon with listen() and removed with unlisten()
change misleading "dataPath" to `settingsPath` in App.java
- settingsPath=~/.local/share/signal-cli, while dataPath=~/.local/share/signal-cli/data
only use FileLock when necessary in App.java, and unlock when appropriate
update documentation