Export AuthenticatingActivity

When trying to authenticate with an NFC tag, I was getting this error: ``W/ActivityManager(  544): Permission Denial: starting Intent { act=android.nfc.action.TECH_DISCOVERED flg=0x30000000 cmp=org.kegbot.app/.AuthenticatingActivity (has extras) } from null (pid=-1, uid=10076) not exported from uid 10077``