Support for enumerating loaded classes on ART

[oleavr]

Continuation of frida/frida-core#75. As described by @dpnishant:

Running the following on Android 5.1.1 on Nexus 5

var classes = Java.enumerateLoadedClassesSync();

throws the following error.

Error: Enumerating loaded classes is only supported on Dalvik for now
    at _enumerateLoadedClasses (gumjs-java.js:172:23)

[oleavr]

Implemented in 5977ceb.

[dpnishant]

Awesome! 👍

[TheCjw]

Cooool.