Disable layout switching if only one layout

[jeremypw]

Fixes #387 (when one layout).

This is a possible way of improving the situation with shortcuts that include Alt + Shift. There are some unanswered questions:

• Should the Switch Layout shortcut be disabled by default when a second layout is added?
• If not, what should be the default shortcut?
• Can a less problematic default shortcut be used?
• Should a warning be given if Alt + Shift (and similar) shortcut is chosen regarding possible impact on other shortcuts?
• Is this shortcut disabled after installation? If not, should it be if there is only one layout? Where is this done?

[jeremypw]

An attempt to fix this in Gala failed - changes are required upstream (Mutter).

[davidmhewitt]

I've not really reviewed the code or tested the functionality yet, but in theory, the idea is sound. However, to answer one of your questions:

Is this shortcut disabled after installation? If not, should it be if there is only one layout? Where is this done?

No, it's not disabled by default: https://github.com/elementary/default-settings/blob/be24c151492bb9115c75bd1a7abc88714240294a/overrides/default-settings.gschema.override.in#L19

https://github.com/elementary/default-settings/issues/4

If it were to be disabled by default, we'd need to look at initial-setup and/or settings-daemon to ensure that it was re-enabled if a user selected two layouts when they created their account.

[danirabbit]

@jeremypw I think I agree with David that we should probably handle this in settings-daemon. That way we can be sure that it's done when the user is first created and we update no matter how the user changes their layouts

[jeremypw]

OK, in that case I'll close this PR. Thanks for having a look at it.