Selective import of Variable Collections and Modes

[six7]

When users are importing variables in the plugin today, we import everything.

Instead, we should make it so that when the user presses Import - in the dialog we already have where we define the Import options, that they can choose which Variable collections and modes (nested under collections) they want to import. This can be done by just doing a call to get available collections once before show the dialog with the import options, and then wait for the user's choice, and then proceed with just those collections.

Likely the import logic itself would need to be changed a bit to not just import everything but rather filter on the collections and modes that we defined prior.