MULTIPLE ROOMBAS: selection mechanism accepts multiple roombas

- roombas can be selected individually or many at the same time. some
  commands give error-popup if no roomba is selected (or if more than
  1 is selected in the case of connect and disconnect)
TEST+FIX: Multiple roomba selection tested + little fixes

- Multiple Roomba selection is now tested with Roomba.
- Moving the velocity slider now doesn't make a stopped Romba to
  move (so it is as it used to be some time ago)
- ANGLECORRECTION made more accurate (using speed 100)