Add --log-file parameter to write logs to separate file

Use logback for more control over the log output

Fixes #845

src/main/java/org/asamk/signal/App.java

@@ -69,6 +69,9 @@ public class App {
         parser.addArgument("--verbose")
                 .help("Raise log level and include lib signal logs. Specify multiple times for even more logs.")
                 .action(Arguments.count());
+        parser.addArgument("--log-file")
+                .type(File.class)
+                .help("Write log output to the given file. If --verbose is also given, the detailed logs will only be written to the log file.");
         parser.addArgument("-c", "--config")
                 .help("Set the path, where to store the config (Default: $XDG_DATA_HOME/signal-cli , $HOME/.local/share/signal-cli).");