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 branch 'raspberrypi_run_python_script' into rfm2pigateway_dev
RFM2Pi Gateway : use Raspberry Pi API

API modifications : - running becomes getrunning
                    - creation of setrunning

rfm2pigateway.py now uses the API instead of a php stub
Simplify get/update settings
RFM2PiGateway : use http or https according to settings
RFM2PiGateway: make logfile and PID file optional

RFM2PiGateway class usability improved: PID file and
logfile not created at __init__ but at instantiation.

Sleep time reduced to 200 ms for increased reactivity.
RFM2PiGateway: Add command line arguments

Make rfm2pigateway.py accept command line arguments:
--no-log-file    log to Standard error stream STDERR (default: log to file)
--show-settings  show RFM2Pi settings and exit (for debugging purposes)
Merge pull request #11 from Jerome-github/rfm2pigateway_dev

RFM2Pi Gateway port to emonCMS dev branch