Cache control headers & query string asset management

closes #1470
issue #1405

- added cache control middleware
- added defaults for all routes, assets, etc
- updated asset helper to add a query string with a timestamp hash to all assets
- added unit tests for asset and ghostScriptTags helpers
- added cache-control checks to route tests
Merge pull request #1798 from ErisDS/cache-control

Cache control headers & query string asset management