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

drivers/Linux/SoftEeprom.h

@@ -6,7 +6,7 @@
  * network topology allowing messages to be routed to nodes.
  *
  * Created by Henrik Ekblad <henrik.ekblad@mysensors.org>
- * Copyright (C) 2013-2017 Sensnology AB
+ * Copyright (C) 2013-2018 Sensnology AB
  * Full contributor list: https://github.com/mysensors/Arduino/graphs/contributors
  *
  * Documentation: http://www.mysensors.org
@@ -37,7 +37,7 @@ public:
 	/**
 	 * @brief SoftEeprom constructor.
 	 */
-	SoftEeprom(const char *fileName, size_t length);
+	SoftEeprom();
 	/**
 	 * @brief SoftEeprom copy constructor.
 	 */
@@ -46,6 +46,19 @@ public:
 	 * @brief SoftEeprom destructor.
 	 */
 	~SoftEeprom();
+	/**
+	 * @brief Initializes the eeprom class.
+	 *
+	 * @param fileName filepath where the data is saved.
+	 * @param length eeprom size in bytes.
+	 * @return 0 if SUCCESS or -1 if FAILURE.
+	 */
+	int init(const char *fileName, size_t length);
+	/**
+	 * @brief Clear all allocated memory variables.
+	 *
+	 */
+	void destroy();
 	/**
 	 * @brief Read a block of bytes from eeprom.
 	 *