Modify workspace next/prev to account for workspaces on all outputs.

Modify workspace next/prev to account for workspaces on all outputs.

Generally, the traversal goes: numbered workspaces in order, and then
named workspaces in the order in which they appear in the tree.

Example:
    Output 1:       Output 2:
	1 3 D C         2 4 B A

Traversal: 1, 2, 3, 4, D, C, B, A, 1, ...

Note, after the numbered workspaces, we traverse the named workspaces
from output 1, and then output 2, etc.