Finish solar terminator

[csete]

Painting of solar terminator and nightshade has been added since v1.3 and there are some remaining issues that should be fixed before it is made available through the user interface:

• [x] Option to disable it
• [x] Make it work with maps centered around longitudes other than 0
• [ ] Re-organize the color settings so that the "Shadow" slider does not come after the terminator settings (Shadow is not related to Global Shadow).
• [x] Integrate with time controller
• [ ] Finalize visual look and feel