[feature] add padded layouts

Merge of padded layouts implementation from @videau, which provides a
way to extend a layout in any dimension by using a neutral element.
5 jobs for padded-layouts in 6 minutes and 9 seconds (queued for 1 second)
Status Job ID Name Coverage
  Style
passed #44971
integration
checkpatch

00:00:44

passed #44970
integration
repoquality

00:00:07

 
  Build
passed #44972
make:generic

00:01:31

passed #44974
knl
make:knl

00:02:23

passed #44973
make:out-of-tree

00:01:29