Initial commit of Select combinations
Merge branch 'hotfix/4566'

Close #4566
Zend\Db\Sql\Select Union Support
Added unit tests
Completed the modifier functionality
Merge branch 'feature/db-sql-select-union' of https://github.com/ralphschindler/zf2 into ralphschindler-feature/db-sql-select-union
Fixed the SqliteMetadata test checking the pdo_sqlite extension
Merge branch 'ralphschindler-feature/db-sql-select-union' into develop