Break out DetectedHBaseEnvironment.create_configuration.

This lets use get new, clean copies of the config.
Add `ApplicationHelper` to locally test coprocessors, other tweaks.

`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`.
Use shared context parameters instead of tunable lets.

Note this obliges us to support module-level file system helpers,
which is fine by me.