header/core: move Listener and Exchange out to the root core pkg

[Wondertan]

The listener works with block data and constructs EDSes, but it is located under the header pkg, which should not depend on share anyhow. Further, the Listener will depend on eds.Store(#1423) which may introduce a dep cycle.

The same is true for the header/core.Exchange

[Wondertan]

This will likely be done by #1304

[tzdybal]

You want me to do it? Or you're going to refactor after #1304?

[Wondertan]

@tzdybal, I was thinking about this issue from a different perspective but realized that your PR touches on it as well and moves those components anyway, so would be nice to move them to the root core pkg

[renaynay]

Already done by #1627