Squashed commit of the following:

- Move tabbed layout for single event to a separate template
- Add layout for a Stages tab
- Populate Event records in in.memory.model with the stages
Merge branch 'master' into frontend_templates
Layout for the stages tab (dev version)
Show/hide the 'New Stage' form
Fixed tabs and 'New Item' form; it's a saved state before solid layout change
WIP: saving changes to WFH