Set default job name in 'submitJobs'

In accordance with what is done for the 'submitJob' method of the
'Batchelor' class, set a default job name of 'None', if no job name is
explicitely specified. This way the 'submitJobs' functions of the actual
implementation can rely on always having this information.
Add documentation to 'submitJobs' method

Add some documentation explaining the arguments and return values of
'submitJobs' of the 'Batchelor' class.