In order to allow mocking for some of the `runner` functions, we created a
separate interface (called `PoolManagerController`) with `Create`, `Get`,
`Delete` operations for the `organization` / `repository` pool managers.
Furthermore, a new runner struct (`poolManagerCtrl`) implements this new
interface. The existing code is refactored to use the `poolManagerCtrl`
whenever the pool managers for `org` / `repo` are handled.
This allows more unit testing for the runner functions since `poolManagerCtrl`
field can be mocked now.
Besides this, there are some typos fixed as well.
