[migration] Fix addition of entity type including boundary constraints on its own attributes This was failing because of the sequence of sql executing when adding an attribute: 1. add entity type <commit> 2. add relation type for attribute 1 <commit> 3. add attribute 1 and associated constraints <commit> etc. In the case of e.g. start/end constraint, we were trying to add the constraint before addition of the constrained attribute (e.g. add constraint on 'start' referencing 'end', but only 'start' has been added yet, not 'end'). This patch fix this by: * adding the relation type to the schema without having to commit, but keeping the operation to revert the addition if necessary - this allows to a single commit for all attributes of the entity type ; * using a LateOperation on constraint operation, so we ensure attributes are actually added before any constraint is added.

[schema sync] Refactor AfterAddCWRTypeHook and AfterAddCWComputedRTypeHook so the latter inherit from the former and enhance their docstring.

Drop embed-allowed option, gone away for a long time

Never record undo information for session or data import for session, it may causes unlimited database size expansion while it makes no sense to undo this kind of changes. For data import, they are created programatically hence we may not want to undo this either.

[cwvreg] load registry using modules names instead of directories Introspect cubicweb, cubes and apphome using pkgutil to generate the full list of modules names for loading registries. Avoiding using bogus logilab.common.modutils.modpath_from_file().

[schema] load schema from modules names instead of directories Introspect cubicweb, cubes and apphome using pkgutil to generate the full list of modules names for loading the schema. Keep historical behavior and check if source .py file exists if a module is found using python bytecode file (.pyc and .pyo) Loading schema from apphome require apphome to be present in sys.path and that "schema" module resolve to a file located in apphome. Update migraction tests to explicitely update sys.path when loading schema from different apps, use a contextmanager for this so it's more readable. Require updated logilab-common and yams

[devtools/test] Skip qunit tests in case of timeout Follow-up on 87443f279b0f where other similar tests got adjusted not to fail (in particular in our CI environment).