[Feature request] Find my phone api

[iMartyn]

I know that this will require extra permissions, but this was the most used ability of my wear watch. With notifications on my wrist, my phone never comes out of silent, but I always know where my watch is.

Also I know this is chicken and egg, no asteroid app means no feature in the sync app but we need both parts. It makes sense to me to make the api here first.