Initial third party F-Droid repo support

Plus various bugfixes
And version increment

lib/app_sources/fdroidRepo.dart

@@ -0,0 +1,81 @@
+import 'package:easy_localization/easy_localization.dart';
+import 'package:html/parser.dart';
+import 'package:http/http.dart';
+import 'package:obtainium/components/generated_form.dart';
+import 'package:obtainium/custom_errors.dart';
+import 'package:obtainium/providers/source_provider.dart';
+
+class FDroidRepo extends AppSource {
+  FDroidRepo() {
+    name = tr('fdroidThirdPartyRepo');
+
+    additionalSourceAppSpecificFormItems = [
+      [
+        GeneratedFormItem(
+            label: tr('appId'),
+            hint: tr('reposHaveMultipleApps'),
+            required: true,
+            key: 'appId')
+      ]
+    ];
+  }
+
+  @override
+  String standardizeURL(String url) {
+    RegExp standardUrlRegExp =
+        RegExp('^https?://.+/fdroid/(repo(/|\\?)|repo\$)');
+    RegExpMatch? match = standardUrlRegExp.firstMatch(url.toLowerCase());
+    if (match == null) {
+      throw InvalidURLError(name);
+    }
+    return url.substring(0, match.end);
+  }
+
+  @override
+  String? tryInferringAppId(String standardUrl,
+      {List<String> additionalData = const []}) {
+    return findGeneratedFormValueByKey(
+        additionalSourceAppSpecificFormItems
+            .reduce((value, element) => [...value, ...element]),
+        additionalData,
+        'appId');
+  }
+
+  @override
+  Future<APKDetails> getLatestAPKDetails(
+      String standardUrl, List<String> additionalData,
+      {bool trackOnly = false}) async {
+    String? appId =
+        tryInferringAppId(standardUrl, additionalData: additionalData);
+    if (appId == null) {
+      throw NoReleasesError();
+    }
+    var res = await get(Uri.parse('$standardUrl/index.xml'));
+    if (res.statusCode == 200) {
+      var body = parse(res.body);
+      var foundApps = body
+          .querySelectorAll('application')
+          .where((element) => element.attributes['id'] == appId)
+          .toList();
+      if (foundApps.isEmpty) {
+        throw NoReleasesError();
+      }
+      var authorName = body.querySelector('repo')?.attributes['name'] ?? name;
+      var appName = foundApps[0].querySelector('name')?.innerHtml ?? appId;
+      var releases = foundApps[0].querySelectorAll('package');
+      String? latestVersion = releases[0].querySelector('version')?.innerHtml;
+      if (latestVersion == null) {
+        throw NoVersionError();
+      }
+      List<String> apkUrls = releases
+          .where((element) =>
+              element.querySelector('version')?.innerHtml == latestVersion &&
+              element.querySelector('apkname') != null)
+          .map((e) => '$standardUrl/${e.querySelector('apkname')!.innerHtml}')
+          .toList();
+      return APKDetails(latestVersion, apkUrls, AppNames(authorName, appName));
+    } else {
+      throw NoReleasesError();
+    }
+  }
+}