Bug fix for content library import+export management commands
This PR fixes buggy Studio management commands:
1. ` export_content_library` command has a file encoding issue. It has been fixed by opening file in binary mode.
2. `import_content_library` command has a string path encoding issue. It has been fixed by using `.encode()` and `decode()` in the right places.
*Studio Updates:* The commands above are working normally
*LMS Updates:* None
Run commands on an existing library with id `<library_id>`. Save it in `/tmp` and import it using `staff` user as owner:
./manage.py cms export_content_library <library_id> /tmp
./manage.py cms export_content_library /tmp/<library_id>.tar.gz staff