D7: Ensure internal media urls start with a slash.

Problem/Motivation

As part of user onboarding, they had internal media that wasn't getting synced.

Steps to reproduce

Proposed resolution

Update to handle slashes better for internal media.

Remaining tasks

1. Update code
2. Review and test
3. Commit :)

User interface changes

API changes

Internal media is included in the seed.

Data model changes