Peel appart make_or_load_nwbfile context manager.

[h-mayorquin]

The make_or_load_nwbfile has led to many errors and difficulties #1138 #1114 #911 #910 #912
Plus, even experienced programmers agree that this pattern is difficult to undersand a view which I strongly agree with.

After providing interfaces and converters with create_nwbfile we don't need this complication for anything other than append mode (opening a file from disk and adding data to it). We should use a normal write without context manager for the other cases.