layouts: use termfair layout for terminals

This layout comes from lain collection of layouts. We import it as a
submodule.
shifty: don't spawn anything when moving window around

If a tag does not exist yet and we send a window it, it will be
created. However, we don't want to spawn anything at this point. Add an
argument to `getpos()` for that.
layouts: display nmaster and ncol when changing them

On some layouts, it can help to have the values for nmaster and
ncol. Use a notification to display them.
shifty: remove unused argument from `getpos()`

Instead, use a generic optional `args` argument and use it to tell we
don't want to spawn anything.