Extensive tests to flask cli

[Dmytro Vitel]

Refactor current extensive tests to flask cli commands for testing.
Starting point was made with flask quiz run command - to run step1. Extend command to run step2 and add command to export data as csv.
The necessity of Extensive tests elimination raised after issue #35 implementation which works with alternatives, not distractors on response submission.

[Dmytro Vitel]

Finished this ticket. Some notes - old extensive tests actually also had errors - student with id 12 contains incorrect json (missing " quote at the end) - which for some reason silently ignored everywhere for extensive tests. But this leads to shift of ids relative to emails. Nevertheless, developed test.sh performs same test as Extensive tests and obtains expected result. Note: diff of csv was changed to diff of DataFrames. Next improvement would be to integrate test into pytest.