Make layout region clearer: items above number of regions just vanish

Add all items to default region instead off "adjust the lengths" when there is just one region available, now items above number of regions just vanish. That behaviour has no sense if layout has only one region (that can hold multiple items) and the number of items has no limit.

Awesome job with supporting the layout module!

One thing I noticed right away when I was testing and showing to a coworker for a site buildout was that it's not clear what regions of a layout that nested items will display under. If there was an indicator, even textual, it would be a big step in helping digest the concept of the layout. In practice it goes in sequential order... for instance:

2 columns:
It goes: 1) Top Region, 2) Left Region, 3) Right Region, 4) Bottom Region

Inspired from " view mode " selection for bricks , and from layout api of drupal core , it will be nice addition to have region selection for child items from the respective layout . It will largely improve user experience for end user as well as site builder can create complex feature based on layout api
— @ron.du