Adding transcription rating feedback

Allow users who have agreed to donate their voicemails to also provide
transcription quality feedback.

screenshot:
https://drive.google.com/open?id=0B9o_KvtLkcuIajVtdFN3Y0Qydmx2NXJYN2N3OVA3N0h5UEdR

Bug: 68712148
Test: manual and new unit tests
PiperOrigin-RevId: 176774942
Change-Id: I08b9afbbefaedfb0de5199038a1d2769bd983855