Doc: Remove uses of START and mark as deprecated

o Remove START from CypherSqlDocIT
o This tutorial should be reworked, for now we just remove any mention of START
o Discourage use of START. Fix Cypher SQL example

signed-off-by: Jakub Wieczorek <jakub.wieczorek@neotechnology.com>
Doc: Rename Cypher endpoint sections in REST guide to make clear which endpoint is old and which is new

signed-off-by: Jakub Wieczorek <jakub.wieczorek@neotechnology.com>
Merge pull request #2746 from boggle/no-start

Discourage use of START
Revert "Revert "More parallellization in the batch importer""

This reverts commit 45b41deb576ca39663cac9dee8cc391421ab764d.
Ring changed to SimplePool, which does not rely on acquire/release ordering