Update target and support libs to SDK 21, fixing compile issues

OpenKeychain/build.gradle

@@ -3,8 +3,8 @@ apply plugin: 'com.android.application'
 dependencies {
     // NOTE: Always use fixed version codes not dynamic ones, e.g. 0.7.3 instead of 0.7.+, see README for more information
 
-    compile 'com.android.support:support-v4:19.1.0'
-    compile 'com.android.support:appcompat-v7:19.1.0'
+    compile 'com.android.support:support-v4:21.0.2'
+    compile 'com.android.support:appcompat-v7:21.0.2'
     compile project(':extern:openpgp-api-lib')
     compile project(':extern:openkeychain-api-lib')
     compile project(':extern:html-textview')
@@ -23,12 +23,12 @@ dependencies {
 }
 
 android {
-    compileSdkVersion 19
-    buildToolsVersion '19.1'
+    compileSdkVersion 21
+    buildToolsVersion '21.1.1'
 
     defaultConfig {
         minSdkVersion 9
-        targetSdkVersion 19
+        targetSdkVersion 21
     }
 
     /*