Add Devise for authentication (needs styling).
Add helper to toggle log-in/out link
 Add ImportsController and connect to SalesImporter

* Create new, show pages.
* Stub show action for now.
Move rspec db cleaning config into Spork.each_run block.

Was seeing spurious errors with db setup/teardown state when testing
through spork.  Moving the DatabaseCleaner setup out of the prefork
block into the each_run block fixed, though i'm not sure why - guessing
it's a quirk of RSpec config object scopes.
Add rake task to init .env file
Introduce Import model to replace ImportSummary DTO.
Implement imports index page to show recent imports.

Removed imports_controller_spec: wasn't providing any real value.  We do
need some integration-y specs but those should be at a higher level,
probably with capybara.