add app signing stuff

app/build.gradle

@@ -5,6 +5,7 @@ apply plugin: 'kotlin-android-extensions'
 android {
     compileSdkVersion 25
     buildToolsVersion "25.0.1"
+
     defaultConfig {
         applicationId "com.simplemobiletools.thankyou"
         minSdkVersion 16
@@ -12,10 +13,16 @@ android {
         versionCode 1
         versionName "1.0"
     }
+
+    signingConfigs {
+        release
+    }
+
     buildTypes {
         release {
-            minifyEnabled false
+            minifyEnabled true
             proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
+            signingConfig signingConfigs.release
         }
     }
 
@@ -41,3 +48,23 @@ buildscript {
         classpath "org.jetbrains.kotlin:kotlin-android-extensions:$kotlin_version"
     }
 }
+
+def Properties props = new Properties()
+def propFile = new File('signing.properties')
+if (propFile.canRead()) {
+    props.load(new FileInputStream(propFile))
+
+    if (props != null && props.containsKey('STORE_FILE') && props.containsKey('STORE_PASSWORD') &&
+            props.containsKey('KEY_ALIAS') && props.containsKey('KEY_PASSWORD')) {
+        android.signingConfigs.release.storeFile = file(props['STORE_FILE'])
+        android.signingConfigs.release.storePassword = props['STORE_PASSWORD']
+        android.signingConfigs.release.keyAlias = props['KEY_ALIAS']
+        android.signingConfigs.release.keyPassword = props['KEY_PASSWORD']
+    } else {
+        println 'signing.properties found but some entries are missing'
+        android.buildTypes.release.signingConfig = null
+    }
+} else {
+    println 'signing.properties not found'
+    android.buildTypes.release.signingConfig = null
+}

signing.properties_sample

@@ -0,0 +1,4 @@
+STORE_FILE=/path/to/your.keystore
+STORE_PASSWORD=yourkeypass
+KEY_ALIAS=projectkeyalias
+KEY_PASSWORD=yourkeypass