Migration from old kaltura plugin to simplekaltura

This does the following:

When visiting the simplekaltura settings page checks if there are any entities that can be imported from the old plugin - creates an admin message with link to the import page if import is possible

Defines an admin import page which details how many entities can be imported, with a button to trigger the import script.

Import script converts the original kaltura entities into simplekaltura compatible entities.  Normalizes the kaltura entry_id for deprecated video mix types.

Retains original owners, metadata, time_created, etc.