Add API and model layer capability for link (URL) files
Add tests for creating and downloading a link file
Make sure link items don't break folder downloads

We add them into the zip file as a file containing the link URL
Delete wrapper item if link file creation fails

Only in the case of parentType = folder
Merge branch 'metadata-edit' into link-files
Slightly different view for link files within item view
Remove grunt-contrib-qunit dependency since we don't use it
Merge remote-tracking branch 'origin/master' into link-files
More consistent styling on plugins page
Address Patrick's feedback
Address Patrick's changes in a way that isn't stupid
Merge pull request #185 from girder/link-files

Link files