Create initial high level wireframe for Marigold splash page

[juliasolorzano]

This issue is for the first round of iteration for the Marigold splash page. We've scheduled the first design review on March 17, which is the deadline for Sprint 3 milestone.

[micahtaylor]

First pass. https://gsa.invisionapp.com/share/WGAWMOWTF#/224166902_Mobile
Plan to incorporate content from synthesis next.