net-im/signal-cli: Include patches bringing B-Bus support

This commit updates dbus-java and its dependencies to 3.2.2, which includes
patches contributed by grembo@, which make signal-cli work nicely with
D-Bus on FreeBSD. It is a great thing because now it is possible to use
various TUI clients for Signal.

Additionally, we include an rc(8) service now, which allows users to run
signal-cli as a system service if they desire to use D-Bus system bus to
talk to signal-cli.

Other changes:

• Make _get-links depend on patch instead of extract (sometimes we need to patch Gradle config files to get the versions we really want).
• Introduce ORIGINAL_BUILD_GRADLE variable for robustness.
• Put some documentation into pkg-message to help users start using signal-cli.
• Set JAVA_HOME in the signal-cli script; it is a bug fix.

Special thanks to: grembo@