[ticket/12274] Load correct T_TEMPLATE_PATH during update

PHPBB3-12274
[ticket/12274] Fix broke/missing jQuery asset paths in update script

PHPBB3-12274
[ticket/12274] Add core.js to the install footer

Required so phpbb var is defined, as it is used in admin.js.

PHPBB3-12274
Merge remote-tracking branch 'vsephpbb/ticket/12274' into develop

* vsephpbb/ticket/12274:
  [ticket/12274] Add core.js to the install footer
  [ticket/12274] Fix broke/missing jQuery asset paths in update script
  [ticket/12274] Load correct T_TEMPLATE_PATH during update