[ticket/12160] Add function to check if phpBB is installed.

PHPBB3-12160
[ticket/12160] Check if phpBB is installed before creating phpBB container.

PHPBB3-12160
[ticket/12160] Move phpbb_check_installation_exists() to functions_install.php

PHPBB3-12160
[ticket/12160] Use phpbb_check_installation_exists() in the other modules.

PHPBB3-12160
[ticket/9725] Create an Azure SQL compatible Schema

Two problems were encountered when installing on AzureSQL:
-Azure SQL does not support the ON clause of T-SQL
-Azure SQL requries a clustered index AKA primary key on all tables

The fix is makeshift; it introduces questionable primary indices, which should be replaced with auto--increment columns.

PHPBB3-9725
[ticket/9725] Add dummy indexes for Azure

SQL Azure requires a primary AKA clustered key on every table.
This adds a dummy INT column to act as key,
avoiding possible duplicate entries.
so that these columns can support bigger (speak: huge) tables

PHPBB3-9725
[ticket/11666] Removing MESSAGE_DELETED..

..in /en/posting.php as it is not used.

PHPBB3-11666
[ticket/12268] Extension finder should not crawl through .git/ of extensions

This new filter ignores .svn and .git directories.
When searching for php classes and template files of extensions
we don't need to look inside these directories.

PHPBB3-12268
[ticket/12268] Use FilesystemIterator::SKIP_DOTS

PHPBB3-12268
[ticket/12268] Do not search in folders starting with a dot

PHPBB3-12268
[ticket/12268] Move class out of extension namespace and rename it

PHPBB3-12268
[ticket/12268] Rename class file to recursive_dot_prefix_filter_iterator.php

PHPBB3-12268
[ticket/12268] Do not use substr but just compare the character

PHPBB3-12268
[ticket/8309] Renaming "Last visit" to "Last activity"

PHPBB3-8309
[ticket/8309] Rename $last_visit to $last_activity

PHPBB3-8309
[ticket/11169] Move module 'prune users' to users category

PHPBB3-11169
[ticket/8309] Moving key to get keys in alphabetical order

PHPBB3-8309
[ticket/10590] Remove confirmation page after posting

PHPBB3-10590
[ticket/12035] Adding link to user posts to ACP page

Adding link of posts behind displayed number of posts of the user

PHPBB3-12035
[ticket/11904] Update explanation for what Allow CDN does

PHPBB3-11904