Update routes and controller actions for Statements

My old routes didn't work with Rails 4, and they actually didn't make a
lot of sense. Not sure what I was thinking. Really what I have is a new
statement form and a create statement action which just directly renders
it's result since it's not being saved in the db and given an id to be
pulled up later.

I haven't tested this change, but I'm guessing it will work. Need to
test.
Use secret_key_base instead of rails secret_token
Replace attr_accessible with strong params
Install bootstrap static assets instead of the LESS versions
Remove less-rails from Gemfile since it's no longer used
Refactor User types from methods to constants
Refactor date range stuff to work even with no contributions
Update link to new path for statements new view
Use blocks for default_scope