GHC left some of the unused imports as `import X ()`

This is achieved by using `stack build --ghc-options=-ddump-minimal-imports`
and looking for the *.imports files.

Remove a bunch of esentially-unused layouts. Now the layouts are:

  - Spiral
  - Mosaic
  - Tall

The bordering layout can add windows along the border of the screen,
that way something like videos or something can be shown in the corner
of the screen.