R1:d7a276346f34

Add a secret board view to Projects

Summary:
Ref T1344. This is //very// rough. Some UI issues:

- Empty states for the board and columns are junky.
- Column widths are crazy. I think we need to set them to fixed-width, since we may have an arbitrarily large number of columns?
- I don't think we have the header UI elements in M10 yet and that mock is pretty old, so I sort of very roughly approximated it.
- What should we do when you click a task title? Popping the whole task in a dialog is…