Tweak read performance instrumentation

Ensure we're really timing everything we're doing for handling a read request.
It seems surprising how fast this is but how slow things can be from the JS
side.
Upd data immediate after a navigation

Rather than add a 500ms delay, don't ever update data during a pan/zoom
operation.  But once the operation is complete update the data immediately.
This substantially improves the feeling of responsiveness.
Get Google API key from a separate file instead of directly in main.py

This makes hacking on main.py without checking in an API key less of a hassle.
Prevent flash of white when switching from read view to base view

While we're waiting for bases to load we should show the reads we have
rather than showing nothing.  This makes zooming more fluid.