Factor-out things that provide components for ZODB stack from software/neoppod/
into component/ZODB/. We switch ZODB 3/4/5 to git checkouts, but used revisions
correspond to ZODB versions we were using before, so this should be a
non-functional change.

We need ZODB to be git checkouts for better control, because we'll want to add
our own patches to ZODB4, for example nexedi/ZODB!1.

If that change will be done, it will be done as a separate step.

We will also need git checkouts to add testing support for ZODB, so that we
could setup automatic testing for this essential-to-Nexedi component on our own
testing infrastructure.