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This option makes the creation of 'package_source' custom target optional,
allowing to build with CMake < 3.11 if it is disabled (default).

(cherry picked from commit 141ea279)

(cherry picked from commit b8f35cbb)

Disabled username with escaped character for LIME X3DH related tests as we aren't ready for that yet

Fixed chat room creation returned value if participants list only contains invalid addresses like ourselves

It fix a crash linked to GC of chatroom on a restarted core

Modification in AccountCreator: the algorithm is not forced in the AuthInfo, in order to let register for an account that has only MD5 password.

Add AuthStack object to try to solve issue 5864 (double auth_info_requested() because of double challenge).
Unfortunately this is not complete, as it creates problems with ProxyConfig erroneously and transciently moving to Failed state.
This will be fixed later.

Fix various things around authentication with SHA-256. Especially it allows to authenticate with SHA256 by supplier an auth info with a clear text password, and algorithm left unspecified.