Update to RSpec 3.0.0

Updates to Rspec 3 and applies transpec gem updates to the test suite.
Streamline and organize RSpec setup.

- Streamline `rails_helper` and `spec_helper` to only include what we
use.

- Move capybara and VCR config to their own files to keep things
organized.

- Delete `.rspec` and add it back to `.gitignore`.
Merge pull request #520 from codeforamerica/519-upgrade-rspec

Update to RSpec 3.0.0