consistent table headlines
separate table columns with two spaces
minor #4435 consistent table headlines (xabbuh)

This PR was merged into the 2.3 branch.

Discussion
----------

consistent table headlines

| Q             | A
| ------------- | ---
| Doc fix?      | yes
| New docs?     | no
| Applies to    | all
| Fixed tickets |

Commits
-------

10b607b separate table columns with two spaces
178a2d6 consistent table headlines
Merge branch '2.3' into 2.5

* 2.3:
  separate table columns with two spaces
  consistent table headlines

Conflicts:
	components/http_kernel/introduction.rst
	reference/constraints/UserPassword.rst
Merge branch '2.5' into 2.6

* 2.5:
  separate table columns with two spaces
  consistent table headlines
Merge branch '2.7'

* 2.7:
  separate table columns with two spaces
  consistent table headlines