Enhanced batch support

Enhanced batch support with:

• Named batches (if no name is specified, all pools are selected).
• Batches for specific operations (mine, test, select).

Also:

• Batches should be stored in batches/<operation>/ folders.
• Each batch should have a list of pools and optional arguments (e.g., test batches might optionally have the list of onion keypairs to be tested).

Example invocations:

./onionmine test-batch [batch-name]
./onionmine mine-batch [batch-name]
./onionmine select-candidate-batch [batch-name]
./onionmine encrypt-selected-key-batch [batch-name]

Batches allows mining operations to be done in stages, like when one receives one list of sites at a time to create and test keys without having to process pools from previous lists.