[ticket/8610] Merging topics does not handle bookmarks correctly

https://tracker.phpbb.com/browse/PHPBB3-8610

PHPBB3-8610
[ticket/12589] Search directly in $directory if it's an absolute sub-path

PHPBB3-12589
[ticket/12589] Fix tests

PHPBB3-12589
[ticket/12589] Add test searching in a non absolute directory

PHPBB3-12589
[ticket/8610] Fix bookmarks when merging all the posts of a topic

PHPBB3-8610
[ticket/8610] Throw an error when the dest topic isn't set

PHPBB3-8610
[ticket/10073] Add a contact administrators page and refactor email forms.

The message to be displayed on top of the email form cannot be configured yet.

PHPBB3-10073
[ticket/10073] Replace board_contact mail with links to contact page

Error pages still contain the email address.

PHPBB3-10073
[ticket/10073] Add Admin contact email template

PHPBB3-10073
[ticket/10073] Use namespaces and fix all class names

PHPBB3-10073
[ticket/10073] Fix code sniffer complain

PHPBB3-10073
[ticket/10073] Global announcements have a forum_id now

PHPBB3-10073
[ticket/10073] Fix grammar in comment

PHPBB3-10073
[ticket/10073] Add doc blocks to new classes

PHPBB3-10073
[ticket/10073] Remove unneccessary todos he config switch is enough

PHPBB3-10073
[ticket/10073] Add @config_text to admin_form

PHPBB3-10073
[ticket/10073] Use get_username_string and correctly sprintf for languages

PHPBB3-10073
[ticket/10073] Fix title for "Email topic"

PHPBB3-10073
[ticket/10073] Fix missing language string

PHPBB3-10073
[ticket/10073] Fix invalid type hint

PHPBB3-10073