Added save to PDF support for the photos:
- Added the 'PDFKit' gem to print to PDF
- Added the 'Unicorn' gem to fix multithreading issues regarding 'PDFKit', which is a new server binary
- Created new action and view for the Photo controller ('Print')
- Added a new layout, for the view mentioned above.
- Altered the asset paths, now throughout the application, the links are absolute, not relative (will require extra config if the app is deployed).
Added a picture thumbnail to the Photo Edit view.