script_manager - on/off button not updating on initial start up

[wpferguson]

If darktable is stopped with script_manager open and on the first page of a collection with a activated script, the script will not show as activated (even though it is running) when darktable is restarted.

[wpferguson]

When I delayed scripts starting (#560) I introduced a timing error between when the buttons in script_manager are populated and when the scripts are actually started.