Update CreateSchemaSqlCollector.php setting default namespace/schema name

The namespace is used as name for the database schema. For SQL Server the default schema name is "dbo" and not "default".
Using use statement for Doctrine\DBAL\Platforms\SQLServerPlatform
Put the responsibility to give the default schema name from CreateSchemaSqlCollector to the Platforms (abstract, sqlserver, postgresql)
Fixed a small mistake where method getDefaultSchemaName was declared as protected instead of public.
Adjusted test CreateSchemaSqlCollectorTest::testGetQueriesForPsql the
default schema name is public for postgresql not default. Added debug
statements to test travis-CI.
Added default namespace when no schema support

The current implementation uses the schema name as namespace name.
Some platforms don't support schema's, but a namespace name still needs to
be present. Added namespace name 'default' when there is no default schema
name.
Changed CreateSchemaSqlCollectorTest.php

Added the supportsSchemas method in the mock because it's being used now.
Updated CreateSchemaSqlCollectorTest.php

supportsSchemas() was already added (see last commit).
So changed expectation from 1 to any.
Merge pull request #376 from flip111/patch-3

Update CreateSchemaSqlCollector.php setting default namespace/schema nam...