Update default.py

Cosmetic changes:

Line 310,311,320: Adding a dialog to indicate that the addon is working/not frozen. Some pages take pretty long (up to 30 secs) to fetch. Meanwhile, showing a dialog is aesthetically good to prove that it's not fozen.

Line 323: Adding unsorted/default sorting method. Some series pages have episode names in unsortable order (e.g. The Amazing World of Gumball). Therefore, using the natural appearance order is more convenient than sorting in the wrong order.

Future feature: Being able to reverse the natural order so that the latter episodes show later in the list. Even more convenient!