Scenarios, alternatives and tool filtering documentation

[DillonJ]

Hi folks,

I feel like this functionality isn't very well documented. I'm working on the SpineOpt documentation at the moment and I think we need something on scenarios, alternatives and tool filters - both from a DB perspective - what they are and how they are used - and from a workflow perspective - how we use scenario and tool filters via the arrow etc. I feel that this belongs in the toolbox documentation.