Added advertisement to levels-screen

polished levels 14 and 16 (world 2)

app/build.gradle

@@ -7,7 +7,7 @@ android {
     buildToolsVersion '27.0.3'
     defaultConfig {
         applicationId 'de.frajul.endlessroll'
-        minSdkVersion 12
+        minSdkVersion 14
         targetSdkVersion 23
         versionCode 6
         versionName '0.6.0'
@@ -26,5 +26,6 @@ dependencies {
     compile fileTree(include: ['*.jar'], dir: 'libs')
     testCompile 'junit:junit:4.12'
     compile 'com.android.support:appcompat-v7:23.1.1'
+    compile 'com.google.android.gms:play-services-ads:15.0.0'
     compile files('libs/simple-xml-2.7.1.jar')
 }