Phs/coprocessor integration test harness

`ApplicationHelper` lets a test create a local runner and accept calls to an askari app while stubbing out the outer hbase environment.  It serves as a way to test coprocessor behavior in hard-to-reproduce conditions.  The example app spec demonstrates it.

Several other tweaks are made:
 *  The key value helper has been moved to `lib` and is now public.
 *  The `schema` macro from the schema helper now only parses and exposes the schema yaml.  The `create_schema` macro has been added to do the rest of firing up the creator tool.
 *  The example app schema has been simplified to make it less url-centric.
 *  The `observer_context` double, being included in the application helper, has become just `context`.
 *  Switch to using shared context parameters instead of tunable lets.