Add dismiss help box functionality

[Douglas-Hong]

Summary

• The help box now has a close button on the upper-right corner and is dismissible.
• The help box can only be shown on these months: February/March for Spring planning, May/June for Fall planning, July/August for Summer planning, and November/December for Winter planning.
• If 30 days has passed since the last time the user dismissed the help box AND the current month is still an active month, then the help box will be displayed again.
• Any feedback is appreciated for the active months and the 30 day dismissal threshold.

Test Plan

• Make sure the help box is never shown during inactive months.
• Change the 30 day threshold to something really small, and see if the help box comes back on an active month.

Issues

Closes #652

[KevinWu098]

lgtm but I'm gonna wait for @KevinWu098 to look before merging since he opened the original issue and there's a bunch of discussion on there I don't wanna read 😅

Agreed, also LGTM but...

Freshmen, who are most likely to need the help box, begin planning in July (possibly even June) and SPOPs occur between July-August, so we might want to toss July on the list of active months as well.

Gotta lookout for us younglings 🙏