Memory leak loading upload_contents

[cmcfadden]

There's an issue where assets with loads of files attached (>500) will eventually hit the php memory limit. This is because getFileHandler() within upload_contents eats ~300k per call, mostly in the doctrine entity.

Right now, we touch that in a lot of places, getSearchData, getAsText, etc.

Ideas? Maybe cache those values on the upload_contents object the first time we touch it, then discard that entity. I think we could mostly do that within the upload_contents entirely.