[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