Add delay before pressure shutoff

[ty19]

After we increased the main valve delay to 1.25 seconds at the most recent Luna test, we had to increase the pressure shutoff interval to 2 seconds or else the pressure shutoff would be guaranteed to trigger. The delay before activating pressure shutoff was hard-coded (i.e. not in a config), so we had to recompile during the test, which is bad.

The relevant files are main_worker.cpp/hpp, config.cpp/hpp, and main.cpp. There should be plenty of existing code that does basically the same thing, so it should be straightforward if you read the code. Don't forget to also add the new value to the ini files.