Add column selection to c-admin-table

[ascott18]

Add the ability to select or deselect which columns to show on a c-admin-table. This will be persisted to localstorage, keyed by the current route pathname.

Other considerations:

• Add a prop that can disable this feature
• Add a prop that allows columns to be specified (for non-c-admin-table-page usages). When specified, defaults the custom selection to disabled.
• Allow the key used for persistence to be passed in (for non-c-admin-table-page usages)