(bug 45029) Transactions for metadata modification.

Have created builders for insertion, removal, and single element replacement.

In adding Document.getMetadata which is nearly identical to Document.getData,
the two functions have been refactored to use a common static method
getDataSlice, with this.data/this.metadata as an argument.

Document.spliceMetadata has been added. It is essentially spliceData with
the data/metadata synchronisation issue.

Metadata cursor position is now tracked in the TransactionProcessor. Cursor
advancement has been moved to a function so the metadata cursor can be reset
every time the data cursor is moved.

There were unhit bugs in the TransactionProcessor run test section, where
the data being loaded into the test documents wasn't always being deep-copied,
and the assert was looking at getData instead of getFulldata (which wouldn't
be able to test metadata changes).

Change-Id: Ieb20ab3e7827bc7ff04148f147da6728eb1eb666
Merge "(bug 45029) Transactions for metadata modification."