remove unnecessary rescues

were interfering with debugging because they don't give the proper stack
trace
better (de)serialization for PropMixin
switch to using postgres
fix incorrect variable
add todo re: responding with JSON on errors in send_cart
add pry-byebug
have cart ID be automatically generated in spec
Merge remote-tracking branch 'origin/master' into 79482896_pg

Conflicts:
	Gemfile
	Gemfile.lock
	app/commands/approval/initiate_cart_approval.rb
	app/commands/approval/update_from_approval_response.rb
	spec/models/property_spec.rb
Merge pull request #67 from 18F/79482896_pg

[#79482896] switch to using PostgreSQL