Add regression tests for #2846
Add regression tests for #2846

1). Add one regression test in 167-workspace_layout.t:
    - Get a fresh workspace
    - Set the layout to something
    - Create windows
    - Try to switch to another layout
    - Check if successful
    - Repeat for all 12 possible transitions
2). Add another regression test in 167-workspace_layout.t:
    - Check that the command 'layout toggle split' works regardless of
      what layout we're using

Airblader/i3-original,stapelberg/i3,i3/i3,Airblader/i3,Airblader/i3,Airblader/i3,Airblader/i3,i3/i3,Airblader/i3-original,Airblader/i3-original,Airblader/i3-original,i3/i3,Airblader/i3-original,stapelberg/i3,i3/i3,stapelberg/i3,stapelberg/i3