Kits: Allow for mutable KitInformation

Mutable KitInformation are those that are supposed to be editable in more
user-accessible places (e.g. like the Mini Target Selector or similar)
than the normal kit options page.

The functionality to display these settings is not part of this patch.

Change-Id: I13446c49abf89eaf739a60dbcd01c97e2144de45
Reviewed-by: Tobias Hunger <tobias.hunger@digia.com>