Separate single scenario and multi-scenario plots

[soininen]

Currently, you can always select multiple scenarios when plotting on the Results page, though some plotting settings are less suitable for scenario comparison. If we had separate single and multiple selection modes in the scenario list, we could use optimized plotting settings for each mode. This would also resolve the inconsistency that the scenario list is single selection when the Summary tab is open. The modes could be separate pages or perhaps a knob on the Results page.

[soininen]

Implemented.