Refactor the recruiter commandline interface

[polvanrijn]

Related to Epic: #6155

It would be good to provide recruiter functionalities in the command line. Where each recruiter get's a separate name (e.g. dallinger prolific <cmd> and dallinger mturk <cmd>)

This will work for functions that are available to all recruiters like:

dallinger prolific cost $study_id
dallinger mturk cost $hit_id

dallinger mturk compensate $worker_id $email $dollars --sandbox
dallinger prolific compensate $study_id $submission_id

But also for recruiter-specific commands:

dallinger prolific pause $study_id
dallinger mturk extend --hit_id $hit_id --assignments $assignments  --duration_hours $duration