stbt control: Use as control recorder with stbt record

A new remote type and a new listener type that connect `stbt control`
with `stbt record` via a file socket, in order to use `stbt control`
to record tests scripts.

Launch `stbt record` as

    `stbt record --control-recorder=stbt-control`

and `stbt control` as

    `stbt control --control=stbt-record`

to connect the two applications.