Define a compound graph for SEDA profiles
This patch defines a compound graph using the compound cube API. It implements a custom IContainer adapter which relies on a 'container' relation linking any contained entity to its container (transitive closure). This relation allow to reference the parent profile in rql expressions as needed by later cset. It's dynamically set in hooks, using raw SQL for performance reason. As we need to use seda_profile_container_def from schema, move it from entities to package's __init__, introducing a dependancy on to-be-release compound 0.3.