Backend: add custom kernel version display support

- place version text in a file named "version" in the root of the zip and it will display after the kernel.string when flashing
- useful in conjunction with build scripts, i.e. a generated version file not actually part of the kernel AK2 repo

META-INF/com/google/android/update-binary

@@ -65,6 +65,11 @@ if [ -f /tmp/anykernel/banner ]; then
 fi;
 
 ui_print "$(file_getprop /tmp/anykernel/anykernel.sh kernel.string)";
+if [ -f /tmp/anykernel/version ]; then
+  ui_print " ";
+  ui_print "$(cat /tmp/anykernel/version)";
+  ui_print " ";
+fi;
 ui_print " ";
 ui_print "AnyKernel2 by osm0sis @ xda-developers";
 ui_print " ";