CDAP-538: Ported procedures of the Purchase app to services.

@ParthGandhi The Purchase app has been updated with services instead of procedures, please take a look.
This should be identical to: https://github.com/caskdata/cdap/blob/develop/cdap-unit-test/src/test/java/co/cask/cdap/test/app/TestFrameworkTest.java#L451

Then when I add it to ``ServiceManager`` itself, it'll be easier to fix all these occurrences.