Merge pull request #445 from bdon/master

fix opening tag help in firefox
Improve highway rendering; render halo in a separate layer
fix regression, rename Apply to Close in inspector
More highway rendering improvements
Create method history.hasChanges
add history.numChanges method.

Use hasChanges/numChanges to toggle Save button and show confirmation dialog when navigating away from page.
make notice not a global var.
Properly refer to iD.ui.confirm