Add wrapper for new ISInfo::annotations method

New annotations method was added recently to ISInfo class by @kolos, but we don't have a Python wrapper for it yet. There is also a ISInfo::getAnnotation method which returns ISAnnotation instance which is a thin wrapper for string, I do not think that we really need it on Python side, that utility can be easily implemented with Python tools. So wrapper annotation() in Python returns a dict with both keys and values being strings.