R1:9437bc019d79

Conpherence - make updating title + picture a dialogue that uses drag and drop upload control

Summary: decent title. Stylistically its probably a bit rough. Also, I think @chad describes an even hotter workflow in T2418. Note this removes the "default image" thing which I don't think makes sense conceptually since by default the image changes to who replied last...

Test Plan: uploaded an image - worked. uploaded a txt file - got ugly errors that file was not supported.

Reviewers: epriestley, chad…