XDCR - log count for transaction docs filtered or modified

XDCR could do a few things when transactions are in play:

1. Filter out ATR documents
2. Filter out actual user documents when there are transactional xattrs within it
3. Modify user documents (strip transactional xattr), and send it

2 and 3 should be exclusive based on settings.

We need to add stats to keep track of these, which will alleviate the supportability effort and eliminate the need to dig through logs