Simplify building and testing via Makefile

Change rebar config such that relx is now handled by a target in the
Makefile, and have the ct make target run a compile. Running tests for
more frequently than building a release.
Add a call to retrieve all tags

Load a design document into CouchDB during initialization which
retrieves all the tags used in the documents. Add more test documents
and test the tags retrieval.

make ct passes