Create new flag auto-update to automate running the upgrade process

[Lisa Seeto]

The process by which Mahara detects and performs an upgrade to the site could be further streamlined optionally.
Currently when an upgrade is detected, it redirects to the mahara/index.php page and provides a
link to the upgrade page that must be manually clicked.

A new config flag "auto-update" could be created that when set to true will direct to the mahara/index.php
where it will perform the usual upgrade checks and if they pass will automatically begin the upgrade and redirect to
the upgrade page without requiring the use of a manual click.