Move inventory window closer to center
Log page load time for debugging

Using Navigation Timing API: http://www.w3.org/TR/navigation-timing/#sec-navigation-timing-interface
Move inventory dialog to its own model, voxel-inventory-dialog

Requires deathcap/voxel-inventory-dialog@49fa8f2396d0b6a1912fe4c769720eb4e5906fca