Provide PHONK apps as sharing target

[dronus]

Would be nice if a PHONK application can be used as a sharing target for other Android apps.

On newer Android OS versions, it seems to be possible that an app manages it's sharing targets - so the PHONK script itself could in some way register as a sharing target, if we provide the API for that.

If not possible, PHONK itself can still provide a single sharing target that can be diverted into the currently running PHONK scripts.