[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/11239] Including username before Overview title

Adding username to the page title to avoid confusion while managing
multiple users in ACP

PHPBB3-11239
[ticket/11071] Add fallback if requested style don't exist

PHPBB3-11071
[ticket/8309] Renaming "Last visit" to "Last activity"

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

PHPBB3-8309
[ticket/7707] Add get_username_string() where possible

PHPBB3-7707
[ticket/11169] Move module 'prune users' to users category

PHPBB3-11169
[ticket/12274] Load correct T_TEMPLATE_PATH during update

PHPBB3-12274