Revert "Revert "Remove media between tests, and push resources to storage for tests that require them""

This reverts commit a3a0a99539d5f3e05a3c5fee156a614f145e9c6f.
Only instantiate the device manager the first time it's needed
Only instantiate the device manager if the target is running an Android build (not desktop builds)
Merge pull request #278 from davehunt/remove-media

Remove media (attempt #2)