Fix for on-error during init - modal window was never appended to the body in order to show to the client
Made session clearing during on-init error more respectful of possible other session objects we probably shouldn't be deleting
Did a once-over to ensure any request to the session object is using it correctly
Split up disabled years per shoreline layer instead of grouped by all layers. This minimizes errors in the off-chance the user will have two shoreline layers up and have the same date in both and disables the date on only one layer but it registers on both layers both in view and calculations.

I am considering doing the same for the grouping column if the caps are different on the two layers, but the chance is very small, especially with future standardization of shapefiles and/or switching the date_ column to a date format