Assorted doc fixes.

• Remove unclear "wiring harness" terminology
• Fix broken troubleshooting link
• Fix troubleshooting page so it either links to a specific page on actuator assembly or at least covers problems with the Viton O-rings. (It also may be time to retire the actuator drilling jig..printers are so much better now, if the actuator hole needs drilling there are probably many other irreparable problems!)

There are quite a number of other instructions fixes to do. But might be good to merge rather than wait.

Closes #363 (closed) #360 (closed)