Indicate that evidence is optional while adding/updating an activity
Make numerous improvements and bug fixes:
- Make the form for adding a new activity manually show up in a modal popup.
- Make the category titles expand/collapse upon click
- Add cancel buttons to cancel out of the form for creating a new activity or updating an existing one.
- Add the jQuery UI date plugin for showing dates and format it in UK format but save in MySQL format.
- Improve the overall experience by adding JavaScript notifications and redirect to base URLs after certain operations.
- Fix numerous pre-existing typos in the HTML.