Replace RXTX-based serial library by one based on JSSC

Development on this was done in https://github.com/gohai/processing-serial-jssc. See also https://github.com/gohai/java-simple-serial-connector for changes to JSSC (not yet upstreamed).
Merge pull request #2093 from gohai/serial-new

Replace RXTX-based serial library by one based on JSSC