pages(session): added method to handle reload resistant page specific data: Liberiva Page can now register session data specific to a page using ISatSession methods (see docstrings for details). Those data can resist a page reload, are specific to a session and a page.

try:
    from common.constants import Const as C
except ImportError:
    pass # import doesn't work at this stage with pyjamas
else:
    __version__ = C.APP_VERSION