Moved App Sources into separate files

lib/app_sources/izzyondroid.dart

@@ -0,0 +1,57 @@
+import 'package:html/parser.dart';
+import 'package:http/http.dart';
+import 'package:obtainium/providers/source_provider.dart';
+
+class IzzyOnDroid implements AppSource {
+  @override
+  late String host = 'android.izzysoft.de';
+
+  @override
+  String standardizeURL(String url) {
+    RegExp standardUrlRegEx = RegExp('^https?://$host/repo/apk/[^/]+');
+    RegExpMatch? match = standardUrlRegEx.firstMatch(url.toLowerCase());
+    if (match == null) {
+      throw notValidURL;
+    }
+    return url.substring(0, match.end);
+  }
+
+  @override
+  Future<APKDetails> getLatestAPKDetails(String standardUrl) async {
+    Response res = await get(Uri.parse(standardUrl));
+    if (res.statusCode == 200) {
+      var parsedHtml = parse(res.body);
+      var multipleVersionApkUrls = parsedHtml
+          .querySelectorAll('a')
+          .where((element) =>
+              element.attributes['href']?.toLowerCase().endsWith('.apk') ??
+              false)
+          .map((e) => 'https://$host${e.attributes['href'] ?? ''}')
+          .toList();
+      if (multipleVersionApkUrls.isEmpty) {
+        throw noAPKFound;
+      }
+      var version = parsedHtml
+          .querySelector('#keydata')
+          ?.querySelectorAll('b')
+          .where(
+              (element) => element.innerHtml.toLowerCase().contains('version'))
+          .toList()[0]
+          .parentNode
+          ?.parentNode
+          ?.children[1]
+          .innerHtml;
+      if (version == null) {
+        throw couldNotFindLatestVersion;
+      }
+      return APKDetails(version, [multipleVersionApkUrls[0]]);
+    } else {
+      throw couldNotFindReleases;
+    }
+  }
+
+  @override
+  AppNames getAppNames(String standardUrl) {
+    return AppNames('IzzyOnDroid', Uri.parse(standardUrl).pathSegments.last);
+  }
+}