Fixed proguard inclusion in gradle and minify in release for plugins

Added doc for Empa proTime

Author: Alebat

SensorFlow/plugins/build.gradle

@@ -9,8 +9,14 @@ android {
         targetSdkVersion 24
         versionCode 1
         versionName "1.0"
+
+        proguardFile getDefaultProguardFile('proguard-android.txt')
     }
-    productFlavors {
+
+    buildTypes {
+        release {
+            minifyEnabled false
+        }
     }
 
     packagingOptions {
@@ -19,7 +25,7 @@ android {
 }
 
 dependencies {
-    compile 'com.android.support:appcompat-v7:24.2.0'
+    compile 'com.android.support:appcompat-v7:24.2.1'
     compile 'commons-io:commons-io:2.4'
     compile 'com.google.code.gson:gson:2.4'
     compile 'com.loopj.android:android-async-http:1.4.6'

SensorFlow/plugins/proguard-rules.pro

@@ -0,0 +1,18 @@
+# Add project specific ProGuard rules here.
+# By default, the flags in this file are appended to flags specified
+# in /home/alessandrobat/android-sdk-linux/tools/proguard/proguard-android.txt
+# You can edit the include path and order by changing the proguardFiles
+# directive in build.gradle.
+#
+# For more details, see
+#   http://developer.android.com/guide/developing/tools/proguard.html
+
+# Add any project specific keep options here:
+
+# If your project uses WebView with JS, uncomment the following
+# and specify the fully qualified class name to the JavaScript interface
+# class:
+#-keepclassmembers class fqcn.of.javascript.interface.for.webview {
+#   public *;
+#}
+-keepattributes InnerClasses

SensorFlow/plugins/src/main/java/eu/fbk/mpba/sensorsflows/plugins/inputs/empatica/EmpaticaNode.java

@@ -31,6 +31,11 @@ public class EmpaticaNode implements NodePlugin<Long, double[]> {
     // also through the values.
     private Long mTimeToDevice = 0L;
 
+    /**
+     * Converts the seconds in nanos and updates TimeToDevice
+     * @param seconds timestamp received in seconds
+     * @return timestamp received in nanoseconds
+     */
     private Long proTime(double seconds) {
         Long nanoTime = System.nanoTime();
         Long nanos = (long) (seconds * 1_000_000_000);