Create a panopoly_test module to hold Views and Content Types for testing

There's two main reasons for this:

• There are things in Panopoly which can't be tested with the content/views currently created during the tests, for example #2154211: Add Behat test for enabling pager and more link in a Views content pane.
• So that we don't depend on panopoly_pages and panopoly_demo for tests that aren't directly testing those modules. The thinking is that changing panopoly_pages should only require updating the tests for panopoly_pages - NOT every test we have. ;-)

We could also use this as a way to package the Panopoly test scripts and Behat features, now that we know child distributions want to use them. But that's further down the line.