Refactored the event.go handler's file

[maernest04]

PR for #118

Problem

For the handlers/event.go folder, the folder was cluttered with every event API such as event reading and writing, getting attendee information, registration and waitlist, and admin registration dashboard information. This made the file way too big and cluttered.

Solution

Separate the handlers/event.go file into separate files, using the same package name "handlers" but separating each event APIs into their own file.

[steeevin88]

can we make a new event folder in here? and then simplify the file names, ex.

handler.go
read.go
write.go
registration.go
admin_registration.go
attendee.go
waitlist.go

[steeevin88]

we should also split the test file too