drop/replace Photo#date_time_original
remove erb layout
add debugging gems
better scoping in photos controller
add linker helpers
link to stuff using linker helpers
DuplicateFinder

* Check for duplicates with hamming distance

Unfortunately this is done in ruby and loads
all objects. There is a postgres extension,
but that won't work on HEROKU.

#improve
add duplicate check to views and controller
threshold range slider