RavenDB-2268 Fixing new prefixed key creation in the tree rebalancer - preventing from doing very long prefix (when trying to add a key that already exists in a page - just rebalancing case when left implicit node is changed) [all voron's tests are green]
RavenDB-2268 Removing a lot of TODOs
RavenDB-2268 Introducing min length of a prefix - 20% of the key size
RavenDB-2268 Better prefix selection
RavenDB-2268 Rounding up the size of a stored prefix to an even number of bytes in order to ensure 2-byte alignment