Spatial analysis improvement: improve UI for area selection

[amyburness]

Need to improve UI to make it easier for users to select areas to compare.
Could be nice to be able to draw multiple reference areas instead of just one and then switch between reference areas.
Could be nice to allow users to select a date for the spatial analysis.
Merging spatial and temporal could be nice. If a user selects multiple dates, then it will be for one area and if they choose multiple areas it will be for a single date.
Analysis could be done for all available periods for all variables for all wanted areas. If this is done and cataloged correctly for a area, then multiple users could reference the same outputs for the same area. It would be caching analyses.