fix(#206): batch size and include docs

[witash]

Adds batch_size and include_docs to couch2pg changes feed request.
small changes to loadAndStoreDocs to use the documents from the changes feed directly instead of requesting all_docs

[witash]

Hi @dianabarsan can you review this?
Do you know why the original couch2pg gets the documents in a separate request? and if there is any reason we shouldn't if it performs better?
Loading documents directly from the changes feed with include_docs=true should be equivalent (in both cases it gets the latest or winning revision) but its not exactly the same...in particular the id is not directly on the change object, but it is on the results from all_docs. So when getting docs from the changes feed, need to get row.doc._id instead of row.id. But it should always be the same...

[medic-ci]

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