WIP: Continue work on input_cache

[TilCreator]

(This pr is mostly for seeing what this fork is doing since that is hard to see on github.)

My fixes are mostly wip, see the TODOs for further information. In my tests I was able to use an unstable sshfs connection (make shure to use the timeout options so that the fs calls actually fail). I also tested with curl / webdav (Remove /src/input/cache/Manager.cxx:97-98 for that), but that somehow still fails even if cached, didn't look further into it.

I will continue working on this, but probably not fast. So help with the TODOs (also ideas how to fix them) and more are welcome.