Create dropdown for committee when creating events

[alexanderqchen]

Motivation

Currently there is no validation on what committee users choose when creating events. This caused a lot of inconsistencies (e.g. ACM-W and W are 2 different "committees").

To Do

• Add a committees section to the config.js file
  This can just be taken from here.

• Add a committee named "General" to this list for general ACM events

• Create a dropdown that allows admins to choose a committee when creating an event
  The options for which committee to choose can be taken from the config.js file (in the committees section you just created).

[alexanderqchen]

#68

[howardwang15]

Assigned to Sai, checkout add-event-dropdown, fix colors on buttons