Add NixCN mobile using flutter

Signed-off-by: Asai Neko <sugar@sne.moe>

mobile/.gitignore

@@ -0,0 +1,44 @@
+# fvm
+.fvm/
+
+# dart
+.dart_tool/
+.packages
+.pub-cache/
+.pub/
+
+# build
+build/
+
+# android build
+.gradle/
+local.properties
+**/android/**/generated/
+**/android/app/debug/
+**/android/app/profile/
+**/android/app/release/
+
+# android keystore
+*.keystore
+*.jks
+
+# ios builds
+ios/Pods/
+ios/.symlinks/
+ios/Flutter/Generated.xcconfig
+ios/Flutter/flutter_export_environment.sh
+ios/ServiceDefinitions.json
+ios/Runner/GeneratedPluginRegistrant.h
+ios/Runner/GeneratedPluginRegistrant.m
+
+# ios personal settings
+*.moved-aside
+*.xcuserstate
+
+# vscode
+.vscode/
+
+# idea
+.idea/
+*.iml
+android/*.iml