Load photo uploader dynamically

Refactor the code in the process (split the button and "controller"
code) and rename/move some of the templates so that it's clear where
they belong.

Initial page load (stable, desktop Chrome) before: 320KB, after: 303KB.

Bug: 48718
Change-Id: I1b167dd27ba0488f99cbd3a29287d8af95011647
Merge "Load photo uploader dynamically"