Added Default customer account logic.

  Paysimple has a class for default customer account, but it
  nothing; so, we are simply going to use customer account in its place.
  Also, added more custom exceptions.
Merge branch 'master' of github.com:/CTA/PS into experiment

Conflicts:
	lib/ps/response.rb
Setting up default customerAccount
Changed how states are called
Merge branch 'master' of github.com:/CTA/PS into experiment

Conflicts:
	lib/ps/exceptions.rb
	lib/ps/response.rb