Fixes h2database/h2database#467 Deadlock between Sequence.flush() and…

* Custom data types handler

* Updated doc, changelog, dictionary. Fixed review comment.

* Extended the custom types handler interface

* Fixed test

* Fixed review comments

* Added note on ABI stability of the feature to docs

to make it more obvious

Updated commercial support information

Use System.nanoTime() to check timeouts

System.currentTimeMillis() is influenced by system time corrections
whereas System.nanoTime() is strongly sequential. So it is better to use
System.nanoTime() when checking for timeouts and elapsed time.

Fix JDBC type of TIMESTAMP WITH TIME ZONE

* Added WITH to CREATE SCHEMA to supply default TableEngine params

* Updated docs to reflect changes in CREATE SCHEMA

* Review fixes - docs; code de-duplication; test for table engine params in schema

* Setter for table engine params in Schema