[ticket/13041] Help_faq.php language file needs to be revised

Todo:
- [x] Reodering "login and registration issues"
- [x] Updating "login and registration issues"
- [x] Updating "User Preferences and settings" 
- [x] Updating "Posting Issues"
- [x] Updating "Formatting and Topic Types"
- [x] Updating "User Levels and Groups"
- [x] Updating "Private Messaging"
- [x] Updating "Friends and Foes"
- [x] Updating "Searching the Forums"
- [x] Updating "Topic Subscriptions and Bookmarks"
- [x] Updating "Attachments"
- [x] Updating "phpBB3 Issues"
- [x] Adjust/correct some answers to be compliant with new phpBB features

This is a WIP PR.
To be discuss.

PHPBB3-13041
Oops it's "Request" and not "On demand"

There are 4 types of group "Open", "Request", "Closed" and "Hidden".
Only the "Request" group can be joined by a member and requires approval.
"Open" is a free access group.
The two others can only be managed by a group leader and members cannot join these groups.
That's why I thought to change this line. But if you think this doesn't make sense I cancel the last commit.

Please, let me know.