Move versioned releases into package subdirectory

This was an error introduced in #1797
Update deps and version constraints for packet and openflow
Add frenetic.2.0.0 release
Update maintainer email address
frenetic: add ocaml version constraint
frenetic: add packet constraint to old versions
frenetic: add ocaml version constraint to old versions
Merge pull request #1836 from seliopou/frenetic

Frenetic Release