categories: init

[MarcelCoding]

closes #267

• each torrent can be associated with a category
• categories must be defined using the cli or env vars
• in the webui categories can be assigned when adding torrent or on a later stage in the details view
• the torrent list can be filtered by categories
• the api also supports filtering by categories, so external application can filter for only their torrents

disclamer: this was implemented using ai

[SuperSandro2000]

@ikatson Could you take a look? Thanks!