MODE-2350 OracleDdlParser update for multi-op ALTER TABLE

Method parseAlterTableStatement now supports basic chained ADD and/or
MODIFY commands. The existing functionality should be the same (ran
tests without issues).

Will do some more coding later to add complete column definitions as
ALTER TABLE MODIFY currently only detects changes that include datatype
modifications.

 * modified parseAlterTableStatement

 * modified parseColumns and overloaded for compatibility

 * created Oracle local parseColumnDefinition

 * hopefuly not broken things (... much)