[ticket/12661] Load extensions templates from "all" folder by render()

PHPBB3-12661
[ticket/12661] Add template test

PHPBB3-12661
[ticket/12661] Add new line at the end  of files

PHPBB3-12661
Merge pull request #2908 from Pico/t/12661

[ticket/12661] Load extensions templates from "all" folder by render()
Merge branch 'develop-ascraeus' into develop