Update stock Homepage to look like Dashboards

Summary: Swaps out AphrontPanels for ObjectBoxes. I'd like to start reducing the floating object lists around the site for consistency. Also, these should provide more items above the fold.

Test Plan:
Test on my local homepage. Built a fake welcome.html too, though I think that's deprecated.

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Reviewers: btrahan, epriestley

Reviewed By: epriestley

Subscribers: Korvin, epriestley

Differential Revision: https://secure.phabricator.com/D11529