XGENTOOLS-1070: Add an onboarding modal for first time visitors of the mms docs

Signed-off-by: Sam Kleinman <samk@10gen.com>
XGENTOOLS-1070: Client-side reloads if the user lands on the wrong version of mms docs

Signed-off-by: Sam Kleinman <samk@10gen.com>
XGENTOOLS-1070: Make the modal prettier, and include an option to not select which version of MMS they want to view docs for.

Signed-off-by: Sam Kleinman <samk@10gen.com>