Allow CREATE TRIGGER BEFORE w/DML

allowing dml is implementation defined, so we might as well parse
it (plus, I don't think the parser is the part of code that should
make that decision)
Support for block trigger
Removed old CREATE TRIGGER NO CASCADE BEFORE

this was derby specific
Added support for instead of trigger time
Removed Derby trigger mode code
Added whenClause, removed whenText
Updated test expecteds
Added a test covering insteadOf & when clause
Added atomic in the the getReservedWords method
Removed db2sql token, now that it's not used
merge ScottDugas: Create trigger before / create trigger block

Merge pull request #153 from ScottDugas/sql-parser/create-trigger-before
https://github.com/FoundationDB/sql-parser/pull/153