[ticket/13126] Improve the feedback when running the migrations

PHPBB3-13126
[ticket/13126] Extends migrator_output_handler instead of using a closure

PHPBB3-13126
[ticket/13126] Move migrator_output_handler to an interface

PHPBB3-13126
[ticket/13126] Change messages verbosity levels

PHPBB3-13126
[ticket/13126] Fix tests

PHPBB3-13126
[ticket/13193] Add link to post count in PMs

PHPBB3-13193
[ticket/13193] Add load_search config check

PHPBB3-13193
[ticket/13193] Make template more readable

PHPBB3-13193
[ticket/13126] Add missing use statement

PHPBB3-13126
[prep-release-3.1.0] Update version to 3.1.0
[prep-release-3.1.0] Prepare Changelog
[ticket/13208] Add security issues to the final changelog

PHPBB3-13208
Merge pull request #3059 from nickvergessen/ticket/13208

[ticket/13208] Add security issues to the final changelog
Merge remote-tracking branch 'Nicofuma/ticket/13126' into ticket/13211
[ticket/13211] Add log wrapper for writing database updater to log file

PHPBB3-13211
[ticket/13211] Move console migrator output handler to db folder

PHPBB3-13211
[ticket/13210] Use the correct config value

PHPBB3-13210
Merge branch 'prep-release-3.1.0' into develop-ascraeus

* prep-release-3.1.0:
  [ticket/13208] Add security issues to the final changelog
  [prep-release-3.1.0] Prepare Changelog
  [prep-release-3.1.0] Update version to 3.1.0
Merge branch 'develop-ascraeus' into develop

* develop-ascraeus:
  [ticket/13208] Add security issues to the final changelog
  [prep-release-3.1.0] Prepare Changelog
  [prep-release-3.1.0] Update version to 3.1.0

Conflicts:
	build/build.xml
	phpBB/includes/constants.php
	phpBB/install/schemas/schema_data.sql
	phpBB/styles/prosilver/style.cfg
	phpBB/styles/subsilver2/style.cfg
Merge pull request #3061 from Elsensee/ticket/13210

[ticket/13210] Use the correct config value

* Elsensee/ticket/13210:
  [ticket/13210] Use the correct config value