[1.7.x] Used link label in models FAQ to ease translation

Backport of d9d924250 from master.
[1.7.x] Fixed #22421 -- Regression in fixtures loading.

Loading fixtures were failing since the refactoring in 244e2b71f5 for
inheritance setups where the chain contains abstract models and the
root ancestor contains a M2M relation.

Thanks Stanislas Guerra for the report.

Refs #20946.

Backport of 862e1ff234 from master
[1.7.x] Fixed #22679 -- Fixed empty tuple serialization in MigrationWriter.

Thanks rockallite.wulf for the report.

Backport of ad994a3c5b5911a12a5e2f2a8d06c036be1b8ad8 from master.
[1.7.x] Fixed #20816 -- Added hints about Django middleware ordering

Thanks gthb Trac user for the report, kolypto StackOverflow
user for the initial list and Tim Graham for the review.
Backport of 756c390fb5 from master.