Summary:
Add a basic breadcrumbs element, and implement it in Paste.
This needs some polish but is most of the way there.
Test Plan:
{F26443}
{F26444}
{F26445}
(This element is not visible on devices.)
Reviewers: chad
Reviewed By: chad
CC: aran, btrahan
Maniphest Tasks: T1960
Differential Revision: https://secure.phabricator.com/D4087
