Bump compile SDK and buildtools version to 26 (Oreo).

Bump the support lib version to 26. This allows for using property
animators (R.animator) in FragmentTransaction.setCustomAnimations.

Add the google maven repo, as from support lib 26 onwards, they're only
publishing it in there.

Bump the gradle version while we're at it, keep Android Studio quiet.

Source/Android/app/build.gradle

@@ -1,8 +1,8 @@
 apply plugin: 'com.android.application'
 
 android {
-    compileSdkVersion 25
-    buildToolsVersion '25.0.2'
+    compileSdkVersion 26
+    buildToolsVersion '26.0.2'
 
     lintOptions {
         // This is important as it will run lint but not abort on error
@@ -71,7 +71,7 @@ android {
 }
 
 ext {
-    androidSupportVersion = '25.3.0'
+    androidSupportVersion = '26.1.0'
 }
 
 dependencies {

Source/Android/build.gradle

@@ -3,12 +3,15 @@ buildscript {
         jcenter()
     }
     dependencies {
-        classpath 'com.android.tools.build:gradle:2.3.0'
+        classpath 'com.android.tools.build:gradle:2.3.3'
     }
 }
 
 allprojects {
     repositories {
         jcenter()
+        maven {
+            url "https://maven.google.com"
+        }
     }
 }