Allow user to crop member photo thumbnails on edit/create

[jgraycar]

Right now, a member's thumbnail displayed on the index/current/alumni pages is auto-cropped, which can lead to some non-ideal images. Let's fix this by allowing the user to crop the thumbnails themselves!

Example bad thumbnails

[jgraycar]

Helpful links:

• Possible gem: https://github.com/rsantamaria/papercrop
• http://railscasts.com/episodes/182-cropping-images/
• http://andowebsit.es/blog/noteslog.com/post/how-to-allow-users-to-crop-images-in-rails-4/
• http://www.odysseyonrails.com/articles/10
• https://www.viget.com/articles/manual-cropping-with-paperclip