bci: Add BCI_AD_MFT_DATA to bci_ad_get()

This patch extends the bci_ad_get() helper function adding a
new AD type for manufacturer specific data.

Usage example:
ret = bci_ad_get(buffer, sizeof(buffer),
		BCI_AD_NAME_COMPLETE, name,
		BCI_AD_MFT_DATA, mft, &size,
		BCI_AD_TX_POWER, &tx,
		BCI_AD_INVALID);
examples/bci-broadcaster: Use bci_ad_put() to assemble data
examples: Add bci-ibeacon example
nrf51822: Add README
examples: Update README
Update README