Added a decorator for plugins to perform work in pyev thread

from functools import wraps

def main_thread(func):

    """Decorator for plugin methods that need to be executed in pyev thread.

    Actually anything that has an attribute `main` that points to an instance of

    MainLoop.

    """

    @wraps(func)

    def decorated(self, *args, **kwargs):

        return self.main.call_in_main_thread(func, self, *args, **kwargs)

    return decorated