server (pages): impleted CSRF protection: A basic CSRF protection has been implemented using CSRF token. The token is created on session creation, and checked on data post. The process should be fully automatic, and a hidden field is added in forms in sat_templates when csrf_token is present in template data (require to import input/form.html with context). If token is wrong on absent, an unauthorized error page is returned (and client ip is logged). Also don't use anymore inlineCallbacks in _on_data_post, as StopIteration exception are catched by inlineCallbacks, resulting in bad behaviour. As a further security, getPostedDate raise a KeyError instead of StopIteration is a specific key is looked for and missing. Added HTTP_SEE_OTHER status code in constants.

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