Handling interrupts

@giulioungaretti is already working on this.

Since May 8, 2017.

Hi all (esp you @eendebakpt @peendebak @MerlinSmiles ),
let's use this issue to fix the problem of handling interruptions.

There are two parts to this problem:

- How to deal with blocking instruments call:

1. Let the instrument finish (at all costs) unless a hard stop is requests (like force interrupt)
2. Break the blocking call, leaving the instrument in a potentially undefined state (if something was request but not read f.ex. of if an command write was interrupted before the entire command was written)

- Where to stop in a loop (but since may people have their own loop that's maybe less important):

1. It does not matter
2. At every sate change ( basically any I/O: send command to instrument, write to disk etc)
3. None of the above