Support OpenEXR with Mipmaps

[pgrAm]

The software seems to support opening mipmaps for KTX & DDS files, showing the file have multiple frames. However OpenEXR can also support mipmaps.

https://github.com/AcademySoftwareFoundation/openexr/wiki/Reading-and-Writing-OpenEXR-Image-Files-with-the-IlmImf-Library/3c62d3b391587008f51cd91cc0b09bdb356942ca

Would it be possible to support opening mipmapped OpenEXR files in the same way as DDS & KTX?