Refactored how TheTVDB api handles exceptions and how those are passed on and handled inside SR core

Fixed app lockup caused by improper handling of TheTVDB errors during image lookups when resource not found.
Re-enabled provider url grabbing from SR API, remove all calls to urls method from __init__ methods of provider classes.
Removed scene name cache, added function to search show cache by terms to retrieve series ID.
Refactored scene exception functions.
Added scheduler job to update scene exceptions once a day.
Tightened up display show view.

Commented out remove_duplicates_from_scene_name_table cache database cleanup function.
Added custom error message when indexer TheTVDB returns 504 HTTP error code.

Refactored episodes attribute on TVShow objects to cache TVEpisode objects and persist.
Refactored usage and removed get_all_episodes method from TVShow class.
Refactored total show size to account for multipart-episodes.
Added delete_episode method to TVShow class to remove episode from shows episode cache.
Refactored usage of TVEpisode class method delete_episode to be called by TVShow method delete_episode instead of directly.
Fixed endpoint call for getting annoucements from SR API.

Added call to save episode data to database after saving episode thumbnail, fixes a database locked issue.

Refactored `_retrieve_show_image` method to download images from fanart.tv if downloading images from indexer fails in anyway.

Refactored dynamic loading of notifier providers.
Refactored dynamic loading of NZB providers.
Refactored dynamic loading of Torrent providers.
Refactored metadata provider config property and added default value.
Refactored web handler arguments to return string instead of None for default value.

Refactored database sessions to use scoped sessions.
Refactored show statistics function to be async.
Refactored relatedEps to related_episodes.

Fixed issue with default not being used with getting attribute that returns NoneType.
Misc issues resolved for adding new shows.

Added ability to disable stripping of special permissions from files.