Address the slew-never-started bug.

There is an occasional issue where align hangs because it waits for a slew to start, but the slew has already started and finished. Thus, align hangs forever. This happens, I believe (and have heard from Wolfgang) because of the parallel processing between ekos and the mount, and always always occurs in a very short slew.

The m_wasSlewStared variable, that is the cause of this, was introduced in July '19 to fix another issue (capturing images while the slew was still ongoing). I believe the system never was never intended to wait long time before the start of the slew--just long enough for the mount to get the message and start slewing. Thus, I've introduced a timer that basically says, "if we've waited 10 seconds, the slew must have started by now." Of course, if the system works properly, as it normally does, it won't wait those 10 seconds. However, in the infrequent cases where the slew start is not detected (usually for short slews) this should fix the issue.