Read date/time from iOS device

This implements reading date and time via the Current Time Service BLE service.

This service is offered by iOS devices and allows to read date, time, timezone and DST information from the central device. At the moment this is done when connecting the first time.

I've tested this with a very old iPad as I don't have access to an iPhone. The issue is that I had do disable almost all current security features to pair with the old iPad and I'm not convinced that the setting of bleDiscCfg is chosen correctly:

/*! Configurable parameters for service and characteristic discovery */
static const appDiscCfg_t bleDiscCfg =
{
  FALSE                                   /*! TRUE to wait for a secure connection before initiating discovery */
};