Sanitize project configuration

Make project compilable out of box. This commit address
the following:
- remove release key
- fix gitignore for Android Studio temp files
- add gradle wrapper properties

V2rayNG/app/build.gradle

@@ -20,34 +20,17 @@ android {
         versionName "1.0.2"
     }
 
-    signingConfigs {
-        release {
-            storeFile file("../key.jks")
-            keyAlias 'ang'
-            keyPassword '123456'
-            storePassword '123456'
-        }
-        debug {
-            storeFile file("../key.jks")
-            keyAlias 'ang'
-            keyPassword '123456'
-            storePassword '123456'
-        }
-    }
-
     buildTypes {
         release {
             minifyEnabled false
             zipAlignEnabled false
             shrinkResources false
-            signingConfig signingConfigs.release
 //            proguardFiles getDefaultProguardFile('proguard-android-optimize.txt'), 'proguard-rules.pro'
         }
         debug {
             minifyEnabled false
             zipAlignEnabled false
             shrinkResources false
-            signingConfig signingConfigs.release
         }
     }
 
@@ -131,4 +114,4 @@ repositories {
     flatDir {
         dirs 'libs'
     }
-}
+}

V2rayNG/gradle/wrapper/gradle-wrapper.properties

@@ -0,0 +1,6 @@
+#Tue Feb 25 12:40:41 CST 2020
+distributionBase=GRADLE_USER_HOME
+distributionPath=wrapper/dists
+zipStoreBase=GRADLE_USER_HOME
+zipStorePath=wrapper/dists
+distributionUrl=https\://services.gradle.org/distributions/gradle-6.5.1-all.zip