Fixed: text shadow on jumbotron for increased readability
Fixed: "Get Started" link on front page

Link was out-of-date, since we renamed "Getting Started" to "Download".
Fixed: mention that Diva is open source on front page

We already mention the plugin system and extensibility under the "Plays well with others" copy above, so I've replaced the corresponding section in the secondary features bar with copy about Diva being open source.

Closes #190