Refactor: BitchatMessage (#610)

* Extract BitchatMessage into a separate file

* Convert `fromBinaryPayload` to `convenience init?`

* Extract message dedup into an extension

* Remove dead `formatMessageContent`

* Minor refactor of timestamp and username formatting

* Remove dead `getSenderColor`

bitchat/Utils/String+Nickname.swift

@@ -0,0 +1,25 @@
+//
+// String+Nickname.swift
+// bitchat
+//
+// This is free and unencumbered software released into the public domain.
+// For more information, see <https://unlicense.org>
+//
+
+import Foundation
+
+extension String {
+    /// Split a nickname into base and a '#abcd' suffix if present
+    func splitSuffix() -> (String, String) {
+        let name = self.replacingOccurrences(of: "@", with: "")
+        guard name.count >= 5 else { return (name, "") }
+        let suffix = String(name.suffix(5))
+        if suffix.first == "#", suffix.dropFirst().allSatisfy({ c in
+            ("0"..."9").contains(String(c)) || ("a"..."f").contains(String(c)) || ("A"..."F").contains(String(c))
+        }) {
+            let base = String(name.dropLast(5))
+            return (base, suffix)
+        }
+        return (name, "")
+    }
+}