"pause" mode when debugging to be able to apply patches

[PVince81]

Sometimes one needs to apply patches after the updater has updated itself.
Instead of doing incredible gymnastics it would be good to have the web UI updater pause after download / after it has updated itself.

Then the admin can manually patch the files on the server for testing.
Then the admin can click "resume" to continue the updater process.

This mode would only be available if "debug" is enabled in config.php.

@VicDeo @LukasReschke what do you think ?