Remove double <?php at top of generated fixture classes.

Fixes #3199
Fix constraints not being included in generated fixtures.

Refs #3200
Improve fixture deprecation warning.

Refs #3200
Use a type that exists when generating tests.

Refs #3202
Tidy up generated fixture code.
Add a test for the table option.

It was missing tests before and was broken.
Merge pull request #3205 from cakephp/3.0-fixture-fixes

3.0 fixture fixes