[prep-release-3.1.0-a3] Update version to 3.1.0-a3
[prep-release-3.1.0-a3] Add migration for 3.1.0-a3
[prep-release-3.1.0-a3] Prepare Changelog
[ticket/11880] Move get_schema_steps function to a migrator helper class

PHPBB3-11880
[prep-release-3.1.0-a3] Commit changelog for 3.1.0-a3
[ticket/11880] migration helper file

PHPBB3-11880
Merge pull request #1995 from EXreaction/ticket/11880

Schema changes can take too long and cause a timeout
[prep-release-3.1.0-a3] Update version to 3.1.0-a4-dev for future development
Merge branch 'prep-release-3.1.0-a3' into develop
[ticket/12167] Allow users to change style via style parameter by default

This change will enable users that don't have the a_styles permission to
preview styles using the style parameter. Using this, they will be able to
use extensions that are or incorporate stylechangers.

PHPBB3-12167
[ticket/12115] Convert user occupation to a profile field

PHPBB3-12115
[ticket/12115] Add language entries for the profile fields

PHPBB3-12115
[ticket/12115] Remove occupation field from html files

PHPBB3-12115
[ticket/12115] Translate profile field name before displaying it in errors

PHPBB3-12115
[ticket/12115] Add methods to interface

PHPBB3-12115
[ticket/12115] Remove old language strings

PHPBB3-12115
[ticket/12115] Also port user interests to profile fields

PHPBB3-12115
[ticket/12115] Add a new migration for profilefield_interests

With this we avoid missing to copy one, when the admin already created
a phpbb_* profile field.

PHPBB3-12115
[ticket/12115] Use base class to reduce duplicate code

PHPBB3-12115
[ticket/12115] Add migration file to remove old user columns

PHPBB3-12115