Wrong 404 behavior on taxonomy listing

No results ≠ 404.

404 must be returned when term does not exist. Not when not results are returned. 

If no results, template says "No posts for {{ term }}".
If term does not exist, then return a 404.
Merge remote-tracking branch 'upstream/master'
Changed abort message.
Test slug against array keys as options can be a slug => Label array
ensure upload controller honours permissions
set the form to false if no permissions
use statements
hide ui
hide ui for files too
leave the add to stack button in place
allow editor to upload files
do not show upload if not allowed
mock the users object so that tests can run without permissions
Revert back to using span instead of button for now
Refine taxonomy behavior:
- When 'behaves_like' like 'tags', return 404 when no content has been found
- When 'behaves_like' like 'categories' or 'grouping', return 404 only if taxonomy slug does not exist
Merge pull request #2322 from rossriley/upload-permissions-fix

ensure upload controller honours file upload permissions
Merge branch 'issue-586' of https://github.com/rarila/bolt into rarila-issue-586

Conflicts:
	app/view/twig/_macro/_macro.twig
git push origin masterMerge branch 'rarila-issue-586'
Merge pull request #2310 from nlemoine/master

 Wrong 404 behavior on taxonomy listing
Renaming '$taxonomy_slug' to '$taxonomyslug'. See #2310