RFM2Pi Gateway: make script daemonizable

- Remove PID management, will be done by caller init script
- Opt-in logging: default logging goes to STDERR,
  optional --logfile parameter allows to pass a file path
- Retry to get settings every 10 sec (in case apache or MySQL
  is not started yet)
RFM2Pi Gateway: Daemonize RFM2Pi Gateway

See readme.md for installation/usage instructions
RFM2Pi Gateway: start/stop, read logs from web GUI
Merge branch 'remoteprotocol_dropdown' into rfm2pigateway_dev
Minor readme update: python dependencies
Fix broken markdown in readme.md
Merge pull request #13 from Jerome-github/rfm2pigateway_dev

RFM2Pi Gateway as a daemon