Add Import/Export functionality

[raxod502]

From @PythonNut on January 12, 2018 7:27

When exporting, we can simply dump the courseList field from the store, either with entries substituted for full course objects ala courses or in a simple text format.

When importing, we will need to validate the input before committing it to the store.

Copied from original issue: hyperschedule/hyperschedule#47

[raxod502]

I'm of the opinion that, going forward, we should not make any assumptions about the well-formed-ness of the course data. That way we can handle mistaken API responses and user input. The current app does not do a great job of this.