If the web server is slow to start, we may need to retry the initial
page load. Implement a retry system that will retry the initial load
4 times, after 1, 2, 3 and 4 seconds, before giving up and leaving
the user with an error message and a link to retry manually.
Upon startup, the runtime will attempt to locate pgAdmin4.py in a
number of different relative locations. Once found, it will execute
it in a new thread. The main window is then created and the brower's
initial page is set to the root of the CherryPy server. At present,
that's http://127.0.0.1:8080.
This runtime implements a brower control with embedded Python
interpretor. The Python interpretor runs a simple script at
startup to generate some HTML that is displayed in the browser.
Arbitrary URLs can be opened from the "Open URL" option on the
File menu.
