MCO-328 reopen logs on signal

With this pull request we add a new optional method on the Logger api, `reopen`, and hook this into SIGWINCH.

SIGWINCH is a little eccentric, but we have already used USR1 and USR2
We'd need to rework all of them I think, as any logging requires a Mutex.

I'll add it to the backlog to change these handlers to ones that raise flags and then handle them in the runloop.