[ticket/11716] Convert Soft Delete Mod to post/topic visibility

PHPBB3-11716
[ticket/11716] Rename migration files and add note that it's converting a MOD

PHPBB3-11716
[ticket/12176] Add functional test for founder deletion message.

PHPBB3-12176
[ticket/12176] Display correct message when trying to delete founder.

PHPBB3-12176
[ticket/9871] Update version check file to use json format

PHPBB3-9871
[ticket/12244] Rename link to Extensions Manager in the ACP

PHPBB3-12244
[ticket/8785] Rebuilding posting_editor pm head + new language vars

PHPBB3-8785
[ticket/8785] Little spaces mistake

PHPBB3-8785
[ticket/8785] Scrollbar to Reciepients and BCC with max-height: 200px

PHPBB3-8785
[ticket/8785] Adds two <hr /> to seperate recipients and BCC

PHPBB3-8785
[ticket/9871] Use $request->variable instead of request_var

PHPBB3-9871
[ticket/9871] Restore get_remote_file

PHPBB3-9871
[ticket/9871] Restore phpbb_version_compare

PHPBB3-9871
[ticket/9871] Mark test as slow

PHPBB3-9871
[ticket/9871] Typehint and comment on var types

PHPBB3-9871
[ticket/9871] Fix tests

PHPBB3-9871
[ticket/8785] Adds a new optical improvement, new file and fixes html bugs

PHPBB3-8785
[ticket/8785] Adds blank lines at file end

PHPBB3-8785
[ticket/8785] <hr /> will only displayed when needed

PHPBB3-8785
[ticket/8785] pm_layout.html back to more standard code

PHPBB3-8785