[server] some pep8 in rql2sql

[dataimport] Deprecate SQLGenObjectStore Closes #10338709.

[datafeed] attempt to acquire synchronization lock even when force is given instead of the implementation in e717da3dc164, raise an error if the lock is already grabbed and catch this error in the caller. See discussion on https://www.cubicweb.org/revision/10790765 Closes #10451635

[schema] Cache RQL expressions on schema loading Add a mapping rql string to rql statement Deserializing schema is ~36% faster with a lot (> 4000) expressions like those generated by cubicweb-container.

[schema] Avoid parsing RQL expressions twice on schema loading Kill full_rql (unnecessary) Use snippet_rql rather than rqlst when possible Don't access to rqlst cachedproperty from __init__ Deserializing schema is ~40% faster with a lot (> 4000) expressions like those generated by cubicweb-container.

[dataimport] Handle Bytes data in ExtEntity and convert them to Binary Closes #13887276.

[test] Avoid assertCountEqual in unittest_syncschema.py It's not clear why this happens, but it seems that assertCountEqual does strange things with unittest2 on Python 2 for equality comparison (trying to sort constraint objects, even though BaseConstraint raise NotImplemented in __lt__ from Yams 0.43). So just avoid using it to get this test passing.

[packaging] Bump version number

[web/session] make sure not to modify an inner value of session.data (closes #11217958) When we modify a mutable value stored in the session's data (dict-like object) we prevent an alternative session data handler (eg. pyramid-redis-session) from detecting this update and synchronizing it in its backend (like redis).

[book] improve a bit the documentation of the database setup also remove the MySQL section.