Change recommended instance selector to store categories as strings

instead of enum

Additional categories can be added, which would cause a crash when
decoding.
As the category isn't used for anything, storing it as an enum value is
not necessary.

Pachyderm/Utilities/InstanceSelector.swift

@@ -51,7 +51,7 @@ public extension InstanceSelector {
         public let description: String
         public let proxiedThumbnailURL: URL
         public let language: String
-        public let category: Category
+        public let category: String
         
         enum CodingKeys: String, CodingKey {
             case domain
@@ -62,20 +62,3 @@ public extension InstanceSelector {
         }
     }
 }
-
-public extension InstanceSelector {
-    enum Category: String, Codable {
-        // source: https://source.joinmastodon.org/mastodon/joinmastodon/blob/master/src/Wizard.js#L108
-        case general
-        case regional
-        case art
-        case journalism
-        case activism
-        case lgbt
-        case games
-        case tech
-        case adult
-        case furry
-        case food
-    }
-}

Tusker/Views/Instance Cell/InstanceTableViewCell.swift

@@ -36,7 +36,7 @@ class InstanceTableViewCell: UITableViewCell {
         self.instance = nil
         
         domainLabel.text = instance.domain
-        adultLabel.isHidden = instance.category != .adult
+        adultLabel.isHidden = instance.category != "adult"
         descriptionTextView.setTextFromHtml(instance.description)
         updateThumbnail(url: instance.proxiedThumbnailURL)
     }