Merge branch 'amiranda/79-add-job_manager-component-to-scord-daemon' into 'main'

Resolve "Add `job_manager` component to scord daemon"

This MR adds a `job_manager` singleton object to the `scord` daemon so that
there's a centralized way of managing the information about jobs registered
in the service. The `job_manager` stores `job_info` objects that allow 
accessing the `job` itself, its `resources` and its `requirements` were they 
needed.

It also updates the `ADM_register_job()`, `ADM_update_job()`, and 
`ADM_remove_job()` rpc handlers and fixes some minor errors with error handling.

Closes #79

See merge request !54