Added offline capabilities.

When SPARK_WLAN_ENABLE is not defined (line 37 in platform_config.h commented), the user application is now able to start. Thanks to Friido on the Forum who came up with the solution. Instead of disabling the LED, which would be susceptible to coming back on with "RGB.control(false);" and wouldn't show what is happening with the Core, I've set pulsing magenta as the color for "offline mode".