portals: Show timepicker for time fields.

[aero31aero]

Show a time picker, preferably https://flatpickr.js.org/ , and attach it to a sample field. The output should be a timestamp that can then be saved in the database.

Necessary steps: Take a look at the edit event form, and its public js scripts in the portal. Attach that timepicker to the startime and endtime fields.

File to make changes to: https://github.com/crux-bphc/fest-manager/blob/pearl/views/portals/event.jade

[ShreyaBits]

I will take up this issue.