Revert "Refactored Config repo to not use singleton"

This reverts commit 05073766649e8bc879383c9a7f79de11543012e3.

Signed-off-by: Mike Barinek <mbarinek@pivotallabs.com>

Conflicts:
	src/cf/api/authentication_test.go
	src/cf/api/routes.go
	src/cf/api/routes_test.go
	src/cf/commands/recent_logs_test.go
	src/cf/commands/space/list_spaces.go
	src/cf/commands/space/rename_space.go
	src/cf/commands/target.go
	src/cf/requirements/service_instance.go
	src/cf/requirements/service_instance_test.go
	src/cf/requirements/targeted_organization.go