Moved zooming code to zooming.js.
- After lockZoomToDefaultCenterPanAtDataCoords, restore (during unlockZoom) to whatever zoom and pan level the user was at before that locking. This will prevent the unexpected behavior in which a user edits while zoomed in, is zoomed out to 1 to edit, the user completes the edit, then next time they zoom, they are snapped back the zoom level that they were at before they started editing.
- Pulled zoom out of setUpZoomOnBoard.