Ajax file uploads - initial

It would probably be a good time to sync, this will also fix the Sponsor attachments issues that people are facing.

Still TODO:
* fix remote links (broken flow since changing attachments to ajax)
* create thumbnails for images (either using sidekiq, or tracking down another solution to carrierwave)
* investigating mime type problem
* make everything slightly prettier
* embed into games page
* allow users to remove attachments

Linked to Issue: https://github.com/MolyJamCollective/MolySite/issues/23