Correct the message in channel mngr in case of ITEM_ALREADY_LOCKED exception

The message is now:

"You cannot edit, copy or move this page because part of the page or target is locked by '{{ lockedBy }}'. Reason : {{ errorReason }}"

However, this is confusing. For example the HST contains the following unit test:

public void test_move_and_rename_succeed_if_a_container_in_backing_page_is_locked_by_someone_else()
throws Exception {

In other words, page and move are supported in case of a container lock. However, if you try to copy the page, you get a ITEM_ALREADY_LOCKED which says the page can also not moved.

ITEM_ALREADY_LOCKED is used for many different cases:

1) page copy not allowed because locked container
2) page copy not allowed because target parent locked by someone else
3) page move allowed because target parent locked
4) page move allowed because a locked child
5) etc etc

With hindsight, the message can only be something generic like:

ITEM_ALREADY_LOCKED = "Your action failed because of a lock exception.
Webmaster '{{ lockedBy }}' holds a lock that prohibits your action.
Reason : {{ errorReason }}"