refactor: move type constants to new media classes

[CyanVoxel]

This refactor is meant to provide an improved interface for determining media categories from file extensions. Instead of relying on searching though lists of extension constants, this refactor provides a new MediaCategory class, which in turn is composed of a MediaType enum, a set of extensions defined by one or more internal sets, and additional data such as IANA registration (more on that later).

The MediaCategory class is then used by the MediaCategories class, which contains every pre-built category used by the program along with the get_types method, which is the new intended way to check for media category membership. Instead of checking if extension .foo is inside a BAR_TYPES list constant, foo is passed to the get_types method which returns any MediaType matches from the extension sets inside of MediaCategory objects added inside the ALL_CATEGORIES list.

While I originally intended to rely heavily on MIME types rather than curated extension lists, it became apparent to me that this wouldn't be feasible for the use cases of TagStudio. There are cases where multiple media categories are desired, such as .csv in both PLAINTEXT and SPREADSHEET categories. In addition, MIME type categories on their own are too limited in scope for some of categorization I'd like to achieve, such as with Office files. With that being said I still wanted the ability to leverage MIME types where possible. The get_types method has an optional flag that when true will leverage the mimetypes module and attempt to guess the media category of an extension if a match was not found in one of the built-in sets. The IANA registration flag within the MediaCategory class is then used to prevent the get_types method from doing unnecessary membership checks inside otherwise unregistered media categories.

TL;DR: New MediaType enums and get_types method to replace the extension list constants with a more flexible system.

[Thesacraft]

I think there's a comma missing here