959967: calculate installed prods correctly

There was a slight issue where we passed in the lastProcessed entitlement
instead of the current one when comparing validity. This caused us to mark
the previous entitlement invalid, and reset the start date in our
calculations.

I've added two new unit tests to test for the bug as well as comment the
complicated method for future devs.
966069: only stack valid ents
Add basic instance based spec tests.
Merge pull request #265 from candlepin/bz959967

959967: calculate installed prods correctly
Merge pull request #268 from candlepin/dgoodwin/inst-spec-tests

Add basic instance based spec tests.
added test
new arch and content arch models
add constructors to Arch
test cases for Arch/ContentArch models
add cp_content_arch to liquibase changelog
Add Arch model and update Content model to use it
fix typo in db add-content-arch db changelog
add get/set arch for Content json model
add contentArch to Content model
get/setters for ContentArch model
add arches to Content model json for ent certs
Add a test arch to the default Content
Add indexes and fk's to liquibase setup
get rid of contentArch join object

setup joinTable relations via hibernate
handle creating contents with an arches list