[merge] backport stable fixes

[cwctl] fix cubicweb-ctl shell command (closes #2583919) * add an uri parsing utility that documents a bit the uri cubicweb supports out of the box * cwctl: use this utility and refactor a bit for clarity (the novelty here being real support for old style 'myapp', or: * 'inmemory://myapp' * 'pyro://pyro-ns-host:pyro-ns-port/myapp' (pyro access through a pyro concentrator) * 'pyroloc://host:port/pyro-instance-id' (direct access to a pyro repository) * 'zmqpickle-tcp://host:port' * dbapi: refactor to sort out some of the complexity and restore functionality lost in 62213a34726e

[ldap test] move the slapd database directory to a tempdir (closes #2583993) This is required to be sure we are not hurt by NFS or such...

[ldap auth] make sure imported passwords from LDAP are encrypted (closes #2583994) When a user is imported from an LDAP source (in ldapfeed or when converting a user from an ldapsource to system one), we may import a clear-text password, which we do not want to do in our system database.

[ldapfeed] don't crash if one specify an unexisting group in the configuration. Closes #2538399

[doc/ldap] update the ldap chapter wrt the ldapfeed source type (closes #2551863)

prepare 3.16

[doc/3.16] complete description of what changed

[rql sources] uses an URL as remote host address for pyro/zmq rql sources, instead of extra configuration parameters. Follows modification of dbapi.connect api. Closes #2539822

[repo sources] move handling of source's url into abstract source as this becomes shared by most sources prepare #2539822