Confirm newer Mimetypes work and add to .desktop associations

Found these while digging around new Mimetypes adopted by EOG:

```
image/x-gray
image/x-icb
image/x-ico
image/x-portable-anymap
image/x-portable-bitmap
image/x-portable-graymap
image/x-portable-pixmap
image/x-xbitmap
image/x-xpixmap
```

Locate the project's .desktop association file and inspect how image MIME types are currently listed. Verify the nine MIME types against the newer types adopted by EOG, then confirm that the association list contains each supported type.

Written by the indexing model from the issue text.