Fixes to various bugs

Fixes the following issues:

1. Rearranged parameter scan controls
2. Observable box now has more room.
3. Models don't have to be loaded to run a parameter scan
4. Time End now matches sample time if sample time exceeded Time End
5. Slider changes in time course simulation no longer delete any overlaid data.
6. Save button in toolbar wasn't responding ("Hittest" was off)
7. Clear plot when a new model is loaded or example selected.
8. Scan wasn't honoring the non-species observables
9. All markers now have filled color, not just data that matches a simulation column name
10. Newly added slider now adds to the top of the slider list.