[ticket/11700] Add develop scripts to use namespaces and rename interfaces

PHPBB3-11700
[ticket/11700] Move all recent code to namespaces

PHPBB3-11700
[ticket/11700] Namespaces and class names should not start with digits

PHPBB3-11700
[ticket/11700] Fix number class names in 3.0.x migrations

PHPBB3-11700
[ticket/11700] Fix avatar tests

PHPBB3-11700
[ticket/11700] Fix config db tests after namespace mishap

PHPBB3-11700