Expand cell_input_hide cells (%hide) when clicked

https://github.com/sagemath/sagenb/issues/135
Merge pull request #181 from paulbrou/master

Expand cell_input_hide cells (%hide) when clicked
unicode box for the "open your browser" message
Merge pull request #182 from fchapoton/master

unicode box for the "open your browser" message
allow groups and others r-x permissions

This fixes the bug in sage-5.4 and later where the user would not
be able to access 3D jmol plots if the server was being run with
a server_pool setup