bci: Add BCI_AD_MFT_DATA to bci_ad_put()

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

Usage example:
    written = bci_ad_put(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
nrf51822: Add README
examples: Update README
Update README
examples: Add bci-ibeacon example