Added possibility to apply "LIMIT 0" in PostgreSQL adapter

This is possible in Postgres and may be useful. "OFFSET 0" seems useless but I think it should be added for consistency.
Use symfony/validator 2.2.*@dev as long as the fix for issue #427 is open.
Added for `namespaced` schema a tablePrexis, otherwise it will overwrite the table from `bookstore`.
Fixed typo
Print now the SQL in the exception in sql:insert command when it fails. Better for debugging.
Added some docBlocks. Added a check against `->getDatabase` before accessing it in getForeignTable().
Added `hasColumn` and some docBlocks.
Added isUnique to Model\Table and some docBlocks.
PostgreSQL requires the keys of the foreignTable of a foreignKeys to be unique.
Fixed missing `use`.
Only parse tables from the schema in $database or in the schema of `search_path`. Fixed `atthasdef` check - it should be boolean.
Added method `applyGroupBy` and `getPlainSelectedColumns` to PDoAdapter that adds the `group by` SQL in Criteria's `createSelectSql`.

PostgreSQL needs to have all selected columns (without aggregate functions) in the `group by` statement.
This fix fills up all selected columns that aren't in the group by statement yet.
Fixed also missing `use`.
Outsourced the commands for the setup of test environment in travis.yml to standalone shell scripts.

Added the PostgreSQL phpunit call.
Removed also --dev since it's the default now in composer.
Typo
Fixed all tests to be multi-db/PostgreSQL compatible.

In detail:
 - added at mysql tests the `mysql` group.
 - fixed some object creations where some fields have no value (but required). that throws otherwise a NOTNULL constraint error in databases that do now automatically converts not-existing values (in inserts) into empty-strings (as mysql it does in NN columns)
 - fixed the test of namespace tests.
 - wrap the most expected SQL strings with a method that converts the SQL to the current db (replaces the quoteIdentifier)
Improved the travis build script a bit.
Moved to the simple folder check as it seems travis doesnt have full bash.
Renamed function declaration to posix-syntax as it seems travis doesnt have full bash.
Added phpDoc to `isUnique`
Fixed #400. Added at all tests the TestCase class as direct or indirect parent class.