Allow .iix file type for images if .iix is in the imageAccept property

**Is your feature request related to a problem? Please describe.**
I am using EasyMDE with ServiceNow and images are stored at paths ending with .iix.
EasyMDE is interpreting these as links.
I understand .iix is not necessarily an image, but in this case I am also explicitly using the "Import an Image" action and I have added image/iix to the imageAccept property of the editor.

**Describe the solution you'd like**
EasyMDE to process .iix link paths as images if .iix is in the imageAccept property

**Describe alternatives you've considered**
There are alternatives in ServiceNow like creating an endpoint that converts requests for /abc.png to /abc.iix and return the result.

**Additional context**
N/A

Start by tracing how the Import an Image action uses the imageAccept property and how EasyMDE distinguishes image paths from links. Verify the behavior with a path ending in .iix and image/iix in imageAccept; done means that path is processed as an image rather than a link.

Written by the indexing model from the issue text.