Function to execute javascript from * lang.

Create a C++ function that will do webkit_execute_script (execute javascript) on the data it's given. This function should be callable from all languages that are plugged into the scripting framework.

Sample use case:

- Bob has his system done in lua, but he uses javascript windows for his chat boxes. His lua function could determine if to send text to a text box if no, and it if should, it can call javascript code to do that.