Render a page template if it exists in a theme for a post marked as page.

Closes #1329.
Merge pull request #1412 from egdelwonk/feature/1329_page_template

Render a page template if it exists in a theme for a post marked as page
Updating Casper to latest inc page template
Move API tests to /integration/

closes #1396
- moved core/test/unit/api* to core/test/integration/api/
- moved core/test/integration/model* to core/test/integration/model/
- moved core/test/unit/utils to core/test/utils
- moved core/test/unit/fixtures to core/test/utils/fixtures/
- changed gruntfile.js to execute api tests with target 'integration'
Merge pull request #1420 from sebgie/issue#1396

Move API tests to /integration/
Add X-Cache-Invalidation Tests

closes #1397
- added checks for x-cache-invalidation to api tests
Merge pull request #1418 from sebgie/issue#1397