pages: fixed cached data when `url_cache` is used: `request.template_data` and `request.data` where cached using a shallow copy, causing trouble when a mutable object was used. This has been fixed by using a deepcopy, which should not be a resource issue as `request.data` and `request.template_data` should contain a few data in most cases.

import os.path

version_file = os.path.join(os.path.dirname(__file__), "VERSION")
try:
    with open(version_file) as f:
        __version__ = f.read().strip()
except NotImplementedError:
    # pyjamas workaround
    __version__ = "0.7.0D"