Feature: Image feature behavior when the file is not found

[Onetchou]

Change the behavior of the image feature when the file is not found:

Options:
a) prompt to locate the file or a different file,
b) remove the image reference from pattern,
c) user can choose to ignore error message but : i) each time the pattern is parsed the error message will popup again, and ii) if the pattern is saved the image reference will be permanently removed.