Attachment flow

Completed with

- [x] UI to display the file attachment widgets  while adding entity and editing entity
- [x] UI to allow uploading multiple files
- [x] List all attached files, on left sidebar or on main details section (value can be set in settings.default.yml of fat-free-crm)
- [x] verify file with type and limited size (value can be set in settings.default.yml of fat-free-crm)
- [x] Deletion of attachments
- [x] Attachments can be saved to either within application public folder or to s3 (s3 credentials can be added in settings.default.yml of fat-free-crm)
- [x] test cases

Can you please verify the changes and let me know if any changes are required.
Thanks :smile: