Revision 1861853

Implemented: The feature where a user will be able to add different types of content(image, document, URL, etc.) to an order.
(OFBIZ-7257)
Here is an implementation plan for the proposed solution. 
Order Attachment Flow:
1) Show 'Attachments' instead of 'Image' on the order view screen.
2) If there are any attachments associated with the order, then their information will be displayed in the form of a button(Content link) else 'No Attachment' label should be shown.
3) If no attachments are there, then along with the label, a button(Add Attachment) will be displayed.
On clicking the Add Attachment button, a user will be redirected to a page where he/she can add different types of content(image, document, URL, etc.) to the order.
Order Attachment Modeling:
Used OrderContent as the entity to store the content and order association.
Created OrderContentType data for an image and document for starters.

Thanks Avnindra Sharma for reporting the original issue, Devanshu Vyas for providing the patch and Jacques for review and suggestions.