Make a datetime_utils file

[khxia]

There seem to be many different places in our repo where we deal with DateTime. Sometimes, these places get their DateTime information in different formats, and they also need their DateTime string in different formats too. Some examples include:

• Workshop Schedule
• Announcements Page
• Home Announcements Banner
• Home Page Countdown

Some of these components already have their own DateTime helper functions. But perhaps it would be better if we had a central datetime_utils.js file where we can just use those helper functions that abstract away all the annoying stuff like formatting and timezones for us such that we don't have to worry about it when dealing with time. This way we would also have a consistent way of how we deal with DateTime instead of having different methods scattered throughout the repo.