Core logic for the importchannel command is migrated to utility functions and all associated tasks updated

[rtibbles]

Currently all the logic for the importchannel command lives inside the management command class. This means that when we want to run an asynchronous task, all it does is end up wrapping the management command in a task, making it harder to test the individual behaviour.

To resolve this, the main logic for actually downloading the channel database and running the import should be abstracted out into separate utility functions in a kolibri.core.content.utils submodule, and then reused in the management command and in the tasks that use it.

[thesujai]

Hi @rtibbles, commenting to claim this issue