implemented custom subject colors for the timetable and unified the color palette system

lib/api/marianumconnect/queries/timetable_get_subjects/timetable_get_subjects_response.dart

@@ -10,10 +10,15 @@ class McSubject {
   final String shortName;
   final String longName;
 
+  /// Persönliche Fach-Farbe (Palette-Name aus [SubjectColor]), serverseitig pro
+  /// Nutzer gepflegt. `null`, wenn für dieses Fach keine Farbe gesetzt ist.
+  final String? color;
+
   McSubject({
     required this.id,
     required this.shortName,
     required this.longName,
+    this.color,
   });
 
   factory McSubject.fromJson(Map<String, dynamic> json) =>

lib/api/marianumconnect/queries/timetable_get_subjects/timetable_get_subjects_response.g.dart

@@ -10,12 +10,14 @@ McSubject _$McSubjectFromJson(Map<String, dynamic> json) => McSubject(
   id: (json['id'] as num).toInt(),
   shortName: json['shortName'] as String,
   longName: json['longName'] as String,
+  color: json['color'] as String?,
 );
 
 Map<String, dynamic> _$McSubjectToJson(McSubject instance) => <String, dynamic>{
   'id': instance.id,
   'shortName': instance.shortName,
   'longName': instance.longName,
+  'color': instance.color,
 };
 
 TimetableGetSubjectsResponse _$TimetableGetSubjectsResponseFromJson(