Sensor upgrade is useful

As promised, the sensor upgrade is now useful in SOAP.   A 3rd navigation mode has been added, which tracks nearby (ish) stars.  Without the sensor upgrade, stellar navigation is unavailable, but each upgrade adds 2,000,000 of sensor range.  If you wander into interstellar space without the upgrade, you can still see and navigate to all the different solar systems like before, but that may change when I find a good compromise between "Player is lost and boned" and "Player is just fine without sensor upgrades" for that situation.

Another closely related change was to the overworld between solar systems.  The solar systems (or solar entry zones really) were named #q, with # being the index in the system stack.  This was great for debugging, but now that we're starting to take interstellar navigation seriously I decided it was time for the solar systems listed in interstellar space to have matching names with the stars at their center.

These additions involved changing a LOT of systems, and crushing a LOT of resulting bugs.  I fear I have not found all of them, but I've at least found the obvious ones.