lumino: allow configuring of the default layout

[oliver-sanders]

Allow users to configure the default tab layout.

Taken from point (1) of #662:

Add a component to the workflow toolbar which allows the current tab layout to saved as the default.

[oliver-sanders]

This should now be relatively straight forward.

Optimistically prioritising.

Note, the "reset layout" button in the "add view" dropdown should restore to this default.

Nice to have: facility for multiple named layouts?