[config] load_configuration should not crash because of fs errors. Closes #2286215

[entity api] unify set_attributes / set_relations into a cw_set method. Closes #2423719 Allowing similar usage as create_entity/cw_instantiate. Update cw code base to remove deprecated calls.

[workflow ui] fix state/transition edition form on existing entity. Closes #2423531 It should not return unrelated entities only in case where the entity exists. Also fix a deprecation warning, vocabulary values should be an unicode string.

[predicates] fix predicates that erroneously evaluate the entity passed as a parameter as a boolean, instead of testing its existence in the keyword arguments -using the kwargs.get('entity') idiom instead of 'entity' in kwargs or similar- ; closes #2424288

[book] fix build warnings/errors. Closes #2430042

[ldap feed] add missing future import

[ldap feed] fix error since with read security activated, password value is not selecteable (closes #2406597). Also add a note in the book about packages required to connect to an ldap server

[config] Set CWDEV, aka dev mode, according to presence of the i18n directory, not .hg

[book] Some tweaks to fix cubicweb-documentation package generation - Fix up PYTHONPATH setting to make sure sphinx can find cubicweb modules - Add a few missing build-dependencies

[webconfig] debug mode should not be special wrt data_url handling (closes #2405487)