Audit Attach File operation

[seanderickson]

Audit the attach file operation (to Screens, Studies, etc.).

• create an audit log of who attached the file and when

@JAS60

[seanderickson]

Note difficulties accomplishing this with the current version of Screensaver:

• handled through the AttachedFiles.doAttachedFile method
• delegates to AttachedFileEntity.createAttachedFile() abstract method implemented per entity (see Screen)
• createAttachedFile does not have a handle on the admin entity
• AttachedFiles does not have a handle on the AuditedAbstractEntity version of the entities it is attaching to, So, this task requires refactoring AttachedFiles.doAttachedFile, and specifically, if keeping with the design goals of SS, AttachedFileEntity should subclass AuditedAbstractEntity in order to get the audit functionality. (this requires database migration as well).