Add setting to determine when to show the integrated console

[daviwil]

Most users probably won't want to see the integrated console immediately as soon as a PowerShell file is opened, so it'd be useful to have a setting to determine whether it should be shown when a PowerShell file is opened.

It's also possible that some people will want to see the integrated console immediately at startup, so maybe this setting should have a few options:

• When requested with "Show Integrated Console"
• When PowerShell file is opened
• When Atom starts

The default would be the first option, but we might present the user with a popup to configure this when they load the package or the first time.