[ticket/10772] Use forum specific style for trigger_error

PHPBB3-10772
[ticket/develop/10772] Unit tests for forum specific style

Unit tests for forum specific style for 3.1 branch

PHPBB3-10772
Merge branch 'ticket/10772' into ticket/develop/10772

* ticket/10772:
  [ticket/10772] Use forum specific style for trigger_error
[ticket/develop/10772] Fix copyright year

PHPBB3-10772
[ticket/10772] Functional tests for forum style

PHPBB3-10772
[ticket/10772] Remove unnecessary comment

PHPBB3-10772
[ticket/8319] Prepend Board URL to LOCAL_URL links to prevent abuse

The description says:
"The URL must be relative to the topic page and cannot contain a server name
or protocol."
We now enforce this and will add a new token with the current behaviour back.

PHPBB3-8319
[ticket/8319] Add new token RELATIVE_URL to allow foreign relative URL parts

PHPBB3-8319
[ticket/8319] Update BBCodes that currently use the LOCAL_URL tag on update

To fix http://tracker.phpbb.com/browse/PHPBB3-8319 we changed the
second_pass_replace value, so that needs updating for existing ones.

PHPBB3-8319
[ticket/8319] Add explanation for RELATIVE_URL and update LOCAL_URL

The explanation now states that links are prefixed with the board URL.

PHPBB3-8319
[feature/twig] Adding Twig dependency to composer.json

PHPBB3-11598
[feature/twig] WIP extension/lexer/some tokenparsers/nodes

PHPBB3-11598
[feature/twig] Support our old INCLUDE statements (no quotes)

Better code for handling IF .blah

PHPBB3-11598
[feature/twig] Working on DEFINE

PHPBB3-11598
[feature/twig] More work on the lexer

Committing what I have now to save it as I'm trying another method next

PHPBB3-11598
[feature/twig] Replace phpBB template code with Twig syntax, then parse w/Twig

Fixing begin token/node, adding includejs token/node

PHPBB3-11598
[feature/twig] BEGIN loops now work

PHPBB3-11598
[feature/twig] Replace phpBB template with Twig

Move phpbb_template class to phpbb_template_phpbb
Changed phpbb_template class to an interface
Switch services.yml to load phpbb_template_twig instead of phpbb_template

PHPBB3-11598
[feature/twig] Language output assignments, using context class again

PHPBB3-11598
[feature/twig] Update composer.lock

PHPBB3-11598