Importing, seeding events, organizations, categories, locations

There's nothing too complicated in this PR, although high-fives for negative lines!

ヘ( ^o^)ノ＼(^_^ )

Anyway, we now have an admin panel and can import datasets of student organizations, leaders, and categories into the database through it. Admins are defined by having `self.admin = true`, and you can promote or demote users with `user.promote` and `user.demote` respectively -- very simple. 

I initially was working on making the seeding tasks (importing organizations and leaders, for instance) a background job. However, it doesn't take long enough to justify starting a worker and we don't want to have to start seed jobs through the console. This way, any admin can do all that through the app.

`rake db:seed` is now much simpler, utilizing the tasks that import data from csv's and the Yale Events Calendar. We can add random subscriptions and other niceties, but it just seems nicer to do it this way, and we get more representative, comprehensive data.