Constrain map zoom and pan to Pittsburgh, start centered on Cathedral

[brlodi]

As discussed in issue #13. This doesn't filter or normalize any data, just constrains the map view to a reasonable area.
The Ghana (0, 0) pin is still lurking out there, somewhere. 😛

[RitwikGupta]

Max bounds could be a little smaller, but this is still great. We can discuss max bounds separately if it's a real issue.

[brlodi]

If the bounds are any smaller, zooming out from the default pan location starts getting jostled around by the bounds before reaching minZoom, and I found that feels really bad.

[vonbearshark]

What if we disallow zooming out past the default? I agree that we should narrow this a little more if we can, and collect the pins that fall outside Oakland to a default