Adding rspec gem for app testing.
Merge branch 'master' into development

* master:
  Adding local_env.yml file import to production.
  Attempt to fix pdf generation error on heroku - update library path
rspec initial setup.
Fixed the 'already initialized constant Mime::PDF' warning.
Added factory_girl gem.
Updated some gems.
Added factory_girl factories for some models: customer, invoice, invoice_item, product.
Added 'invoice' spec stub with 3 tests.
Added 1 test: invoice total.
Added a popup message to notify visitors that estimates are under construction.