Remove the inner and outer borders

The concept of triple border was initially introduced to solve the
visibility problem occurring when the border's environment is similar to
the border itself. In practice however, it doesn't help much and has no
redeeming aesthetic value.
Differentiate focused and active colors
Update TODO
Quick desktop preview

If two identical *use* messages are received, the last one will be
equivalent to *alternate_desktop*.
Be explicit regarding the license
Be neutral
Update TODO
New message: 'flip'