[repo] Add a publish/subscribe mechanism for inter-instance communication using zmq
Each repo can have a publishing and any number of subscribing sockets
whose addresses are specified in the instance's configuration. An
application or cube can subscribe to some 'topics', and give a callback
that gets called when a message matching that topic is received.
As a proof of concept, this introduces a hook to clean up the caches
associated with the repository when an entity is deleted.
A subscription is added using Repository::zmq::add_subscription;
the callback receives a list representing the received multi-part
message as argument (the first element of the message is its topic).
###############################################################################
#
# Put here information about external resources / styles used by your cube,
# or to overides existing UI properties.
#
# Existing properties are available through the `sheet` dictionary available
# in the global namespace. You also have access to a `data` function which
# will return proper url for resources in the 'data' directory.
#
# /!\ this file should not be imported /!\
###############################################################################
# CSS stylesheets to include in HTML headers
# uncomment the line below to use template specific stylesheet
# STYLESHEETS = sheet['STYLESHEETS'] + [data('cubes.%(cubename)s.css')]