Add a "Try it" link to the front page

[Asheesh Laroia]

With this change, visitors to the MediaGoblin site can try a live
instance.

For context, the demo is hosted on a demo server run by Sandstorm
Development Group, which runs the FLOSS Sandstorm software. The path
component in the URL is the app ID, so when new versions are uploaded
to that server, this link will automatically update to install those
new versions.

The Sandstorm "port" of MediaGoblin has the source code available for
its fork here: ​https://github.com/jparyani/mediagoblin/ and links to
it in the footer, as a general good practice and also as a way of
complying with the AGPLv3.

It uses target=_blank because, in my manual testing, after clicking
this link and playing with the MediaGoblin demo, the default thing to
do is to close the tab/window. It would be nice if the MediaGoblin
website were still waiting for me so I could be reminded that I tried
the demo to convince myself that I want to actually install
MediaGoblin.

[Asheesh Laroia]

I've attached a patch in "git format-patch" format.

There is also a branch available for your review here: ​https://gitorious.org/mediagoblin/paulproteuss-mediagoblin-website/commits/a2abd8361e2fe6a6b832544c59c0b3906e50ef9e

Thanks! Let me know if you have feedback or questions or need anything else from me.

[Matt Molyneaux]

This is a really good idea!

[Asheesh Laroia]

Thanks to Chris Webber for merging this and deploying it already!

And hooray, glad you like it moggers87! Please give the demo a try, and see what you think! I'm one of the developers of Sandstorm and am always eager for feedback.