use environment variable in ocr/printer project manifest

[rabbah]

The OCR example which adds slack notifications should use an environment property in the project manifest instead of parameters.

demo-projects/ocr/project-slack-notification.yml

Lines 12 to 14 in bd922f8

	actions:
	- name: slack
	parameters: ${<.slack-env}

This is also needed for the Printer demo.

demo-projects/printer/project.yml

Lines 10 to 12 in bd922f8

	actions:
	- name: notify
	parameters: ${<.slack-env}