Release 20P: Initiate the caller package checking system

Thanks to @bigrushdog for the original code from his no-root algorithm.

Change-Id: I5fc9d671cb6dd33067ae38c0c1d2dafc8599db2c
(cherry picked from commit 1c402c5e4385b2fe19c3b1a6da30c57974c577f7)
diff --git a/app/build.gradle b/app/build.gradle
index fee93e1..265096a 100644
--- a/app/build.gradle
+++ b/app/build.gradle
@@ -21,7 +21,7 @@
         minSdkVersion 21
         targetSdkVersion 23
         versionCode 20
-        versionName "twenty"
+        versionName "twenty - procyon"
     }
 
     buildTypes {