This creates a root.c and moves bits and pieces from elsewhere into it.
* layout_init has been renamed to root_create and moved into root.c
* root_destroy has been created and is called on shutdown
* scratchpad code has been moved into root.c, because hidden scratchpad
containers are stored in the root struct
Implements the following commands:
* move scratchpad
* scratchpad show
* [criteria] scratchpad show
Also fixes these:
* Fix memory leak when executing command with criteria
(use `list_free(views)` instead of `free(views)`)
* Fix crash when running `move to` with no further arguments
