Define tasks for Opora

[KrzysztofMadejski]

Tasks:

• Choose pages containing mentioned tables [find_tables]
• List IDs of transactions on a page X [get_transaction_ids]
• Retype transaction Y [get_transaction]

Create an abstract interface/class ITask/AbstractTask that will be implemented (by let's say DoSomethingTask) and will have methods such as:

• get_form() -> returns by default 'forms/do_something.html' or forms/DoSomethingForm.py
• verify_data (how to code it?) -> [yes/no/partly, confidence, verified_data]
• save_verified_data(yes/partly, confidence, verified_data)

It would be a specific implementation of #83 configuration flow - "How to define tasks?"

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Verifying data

AbstractTask::verify(task_runs) - by default it implements verification by equals on all fields

• one can override whole verify or could implement verification rules for each field, such as
• verify_transactionid_list that would check for equal unordered set
• verify should be aware someone might override individual fields
• for inspiration check https://docs.djangoproject.com/en/1.10/ref/forms/validation/