Add free trial messaging to getting started page and index page

Created by: rrhyne

Campaigns will be free to trial without restriction for one release. We need to ensure customers are aware campaigns will be a paid feature in the future. Additionally, we need to alter customers to the fact that all users can now use campaigns.

This design addresses both concerns:

https://www.figma.com/file/rkxG6h3WzW0rzmPBE0CSbM/Licensing?node-id=0%3A1&viewport=184%2C-538%2C0.5