Add Timber library for logging

The idea is to add a Tree that can save the log to a file which can be
enabled from the settings.

android_app/app/build.gradle

@@ -57,6 +57,9 @@ dependencies {
     annotationProcessor 'android.arch.persistence.room:compiler:1.0.0'
     androidTestImplementation 'android.arch.persistence.room:testing:1.0.0'
 
+    // Timber
+    implementation 'com.jakewharton.timber:timber:4.7.0'
+
     // Local unit tests
     testImplementation 'junit:junit:4.12'
 

android_app/app/src/main/AndroidManifest.xml

@@ -15,6 +15,7 @@
         android:allowBackup="true"
         android:icon="@drawable/ic_launcher_openscale"
         android:label="@string/app_name"
+        android:name=".core.Application"
         android:theme="@style/AppTheme_Light" >
         <activity
             android:name=".gui.MainActivity"

android_app/app/src/main/java/com/health/openscale/core/Application.java

@@ -0,0 +1,33 @@
+/* Copyright (C) 2018 Erik Johansson <erik@ejohansson.se>
+ *
+ *    This program is free software: you can redistribute it and/or modify
+ *    it under the terms of the GNU General Public License as published by
+ *    the Free Software Foundation, either version 3 of the License, or
+ *    (at your option) any later version.
+ *
+ *    This program is distributed in the hope that it will be useful,
+ *    but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *    GNU General Public License for more details.
+ *
+ *    You should have received a copy of the GNU General Public License
+ *    along with this program.  If not, see <http://www.gnu.org/licenses/>
+ */
+
+package com.health.openscale.core;
+
+import com.health.openscale.BuildConfig;
+
+import timber.log.Timber;
+
+public class Application extends android.app.Application {
+
+    @Override
+    public void onCreate() {
+        super.onCreate();
+
+        if (BuildConfig.DEBUG) {
+            Timber.plant(new Timber.DebugTree());
+        }
+    }
+}