Update gradle to 3.0, gradle android plugin to 2.2-beta2

Also needs java8, hopefully only for compilation though
(we need java7 for KitKat)

This also fixes lots of exceptions in the pmd report.

app/build.gradle

@@ -43,6 +43,10 @@ android {
     }
 }
 
+pmd {
+    toolVersion = '5.5.1'
+}
+
 dependencies {
 //    testCompile 'ch.qos.logback:logback-classic:1.1.3'
 //    testCompile 'ch.qos.logback:logback-core:1.1.3'

build.gradle

@@ -5,7 +5,7 @@ buildscript {
         jcenter()
     }
     dependencies {
-        classpath 'com.android.tools.build:gradle:2.1.3'
+        classpath 'com.android.tools.build:gradle:2.2.0-beta2'
 
         // NOTE: Do not place your application dependencies here; they belong
         // in the individual module build.gradle files

config/pmd/pmd-ruleset.xml

@@ -33,7 +33,10 @@
         <!-- Espresso is designed this way !-->
         <exclude name="TooManyStaticImports" />
     </rule>
-    <rule ref="rulesets/java/logging-java.xml" />
+    <rule ref="rulesets/java/logging-java.xml">
+        <!-- disabled because of lots of NullPointerExceptions -->
+        <exclude name="InvalidSlf4jMessageFormat"/>
+    </rule>
     <rule ref="rulesets/java/braces.xml" />
     <rule ref="rulesets/java/strings.xml" />
     <rule ref="rulesets/java/basic.xml" />

gradle/wrapper/gradle-wrapper.properties

@@ -3,4 +3,4 @@ distributionBase=GRADLE_USER_HOME
 distributionPath=wrapper/dists
 zipStoreBase=GRADLE_USER_HOME
 zipStorePath=wrapper/dists
-distributionUrl=https\://services.gradle.org/distributions/gradle-2.14.1-all.zip
+distributionUrl=https\://services.gradle.org/distributions/gradle-3.0-all.zip