Limit photo selection to images. Fixes #296.

This generally makes the file picker only accept image types. The
backend does additional checks since this cannot be relied upon.
Add name to user url
Move plot views together in file
Factor out scoped plot retrieval or 404
Add translation
Audit provide details when instance not found

This function requires instance to be set in order to avoid a runtime exception, but previously did not provide a meaningful exception. I ran into this while implementing delete_with_user on Plot and Tree.
Don't reuse variable names
Add support for deleting plots and trees on server

addresses #882 on github.
Merge pull request #933 from steventlamb/topic/delete_trees_backend

Topic/delete trees backend
Provide a UI for getting detail links for audits

Fixes #875
Merge pull request #918 from ahinz/fix/296/limit-to-images

Limit photo selection to images. Fixes #296.
Merge pull request #937 from ahinz/fix/875/audit-details

Provide a UI for getting detail links for audits
Display custom logo on edits page. Fixes #876.