[Android] Added tools (unix bash scripts) to recompile Android extlibs

For some reason, one might want to recompile the extlibs but this is a tedious task. That's why these scripts are provided.
Please read readme.txt before using them!

tools/android/clean_all.sh

@@ -0,0 +1,6 @@
+#!/usr/bin/env bash
+
+rm -rf tmp
+rm -rf build
+rm -rf src
+rm -rf toolchains