Fix EZP-23390: IOService loads whole file to get mime type

Does not affect Legacy using DFS as it sets it from meta data, however all other handlers are affected.
Depends on https://github.com/ezsystems/ezpublish-legacy/pull/1082 (merged)
Remove InMeory IO handler (not activly used anymore)
Merge pull request #1011 from ezsystems/cluster_mimetype_EZP-23390

EZP-23390: IOService loads whole file to get mime type