Enable flagging of individual images

[sarahpearson]

My thought is the button could say "I don't want to see this," and if someone clicks it, we automatically hide the image from that user permanently.

If clicked for 3 images by same person, we block that person from the user completely (none of their photos shown to the user).
If an image is clicked by 3 different people, then hide that image from everyone.
If a single user gets flagged XX number of times, suspend their account.

[perpetuatingcuriosity]

Cool sounds good! We’ll need some work on the back-end for this. Dependent on #319 @mattl

[rheaplex]

Enabled flagging in the API in 7a2f3d8 .

Photo listing and galleries now do not show blocked images, as described.

User blocking is not yet implemented as described.