Sort scriptable classes array in BeyondGlobal.scala

To avoid conflict in the future.
Use ScriptRuntime to get Array[Byte] in ScriptableCrypto.

A JSArray element can't be casted to Array[Int] directly.
Move the default encoding to BeyondConfiguration.

Encoding would be used quite often in the future, so it'd be
better to have one shared configuration here.
Implement ScriptableBuffer.

ScriptableBuffer is an implementation of `Buffer` class in Rhino.
It basically provides methods to manipulate buffers with String and
Byte. An example code representing the usage of the class is also
added in the `examples` directory in plugins.