make sample dataset + populate test database

[epogrebnyak]

To familiarise with CRUD API need to update database to content more similar to production

[epogrebnyak]

Must define the data source for a mock database

[tinivir]

@epogrebnyak Are we talking about real database structure instead sample we have now? So we should define all components we need to store and their relations.

[epogrebnyak]

@tinivir - a kind of small dataset that we can use in tests, and replace existing values like. Myself and @zarak we'll try to make this small dataset. As a note for myself there are two places for 'good' datapoints elsewhere in the project:

• results of get_data methods in https://github.com/mini-kep/parser-template/blob/master/parsers.py
• https://github.com/mini-kep/intro/blob/master/pipeline_demo.py#L79

As for relations and components we leave just one table/class Datapoints now, no other tables/relations.