Prepare for release-2.13 betas

Author: mikehardy

AnkiDroid/build.gradle

@@ -41,8 +41,8 @@ android {
         //
         // This ensures the correct ordering between the various types of releases (dev < alpha < beta < release) which is
         // needed for upgrades to be offered correctly.
-        versionCode=21300128
-        versionName="2.13alpha28"
+        versionCode=21300200
+        versionName="2.13.0beta0"
         minSdkVersion 16
         //noinspection OldTargetApi - also performed in api/build.fradle
         targetSdkVersion 28