Add config option to skip clear_helpers

[denny]

Adds a config option to skip the clear_helpers call in the base controller; fixes my issue #315

[ankane]

Hey @denny, thanks for the PR! Blazer views aren't designed to wrapped in application templates, so don't want to add an option for it, but you can probably add the helpers back manually if needed.

[ankane]

Cleaning up PRs

[denny]

In case anybody else does trip over this, here's what I have in my ApplicationController now:

def self.clear_helpers
  super unless self == Blazer::BaseController
end

(Pretty sure I wouldn't want anything else to do it either, but I figured it was safest to override the minimum necessary for now.)