Upgrade dependency to Spring Social 1.1.0.M4; Upgrade to Jackson 2; Add support for...

... videos; use String for keys instead of int;

I'm not terribly Gradle savvy, so I left most of that alone. I notice, though, that other Spring Gradle projects are moving away from the submodule model.

A bit of work remains to bring it up to full Spring Social 1.1 compliance, like schema and Java config support.

Please let me know if you intend to use this patch or whether I should move forward with my own fork. Thanks for your efforts and I hope this is of use to someone else...