Linux: Use config file for gateway settings (#1061)

- The following settings can be use on the config file:
  - verbose=[debug,info,notice,warn,err] - Logging verbosity.
  - log_file[0|1] - Enable logging to a file.
  - log_filepath=(FILE) - Log file path.
  - log_pipe=[0|1] - Enable logging to a named pipe(aka fifo).
    Use this option to view your gateway's log messages from the
    log_pipe_file (defined below).
    To do so, run the following command on another terminal:
    - $ cat "log_pipe_file"
  - log_pipe_file=(FILE)
  - syslog=[0|1] - Enable logging to syslog.
  - eeprom_file=[/etc/mysensors.eeprom]
  - eeprom_size=[1024]
- Change some mysgw parameters:
  - Added:
    - -q, --quiet:  for quiet mode, disable log messages written to the
    terminal.
  - Removed:
    - -d, --debug: removed, log messages are now enabled by default.
  - Replaced:
    - -b, --background: replaced by --daemon
- isatty() is no longer used, log messages by default are printed to
  stderr unless the gateway is started with --quiet (#1022)
- MY_LINUX_CONFIG_FILE: no longer holds the path to the eeprom file,
  but to the configuration file

configure

@@ -37,7 +37,7 @@ Installation options:
 
 MySensors options:
     --my-debug=[enable|disable] Enables or disables MySensors core debugging. [enable]
-    --my-config-file=<FILE>     Config file path. [/etc/mysensors.dat]
+    --my-config-file=<FILE>     Config file path. [/etc/mysensors.conf]
     --my-gateway=[none|ethernet|serial|mqtt]
                                 Set the protocol used to communicate with the controller. [ethernet]
     --my-node-id=<ID>           Disable gateway feature and run as a node with the specified id.