Reinstates a batching page cache for batch import

Basically it's the "page cache" version of
https://github.com/neo4j/neo4j/blob/2.1.2/community/kernel/src/main/java/org/neo4j/unsafe/impl/batchimport/store/BatchFriendlyWindowPoolFactory.java

such that there's only one page per store in memory all the time and it
moves along with the batch importer "cursor", no other store file memory required.
The idea with `rewind()` is to make the next call to `next()` position the cursor that the page id that was given as the starting page to the `io()` call.