Improvements for 'Local' and 'C2PAP'

Changes benefiting mostly 'Local':
A 'shutdown' method was added, which can be called in the end of a program using batchelor. At the moment, this is only used with the 'Local' option, in this case it is made sure that queued jobs will still run, and that the sub-processes are cleanly exited (removing a number of error messages that previously appeared at the end of the program).
In the course of this, the usage of 'self' to access the data controlling the processes has been reviewed and fixed in a number of places.

Changes benefiting mostly 'C2PAP':
A 'submitJobs' method was added, taking a list of new jobs with the same arguments that would otherwise be given to 'submitJob' for each single job. This might reduce overhead on a few clusters. For C2PAP use a process pool to run the submit program in parallel. (Unfortunately I could not test this for real.)
In case 'submitJobs' is not implemented for an option, batchelor will itself take care to call 'submitJob'.
Could you please add a comment line detailing the format of `jobs` and the format of the return value, mentioning the "-1" convention for a failed job submission? Thanks!