Use php interface to get gateway settings

- Creation of rfm2pigateway_interface.php
- Modification of gateway : use php interface to get settings or update status,
  no more direct DB access
- Fix "make remote server optional"
- Move PID and log files to new directory, htaccess protected (we don't want
  to expose the logs as they contain apikeys)
Improve logging levels and fix serial port error message
Bugfix : Make path to generated files relative

- Bugfix : Log files and PID file paths are relative
- Increase log size to 2 x 5 Mo
Merge pull request #10 from Jerome-github/raspberrypi_run_python_script

RFM2Pi Gateway