Admin Copy Subtree feature

*Title: Admin Copy Subtree feature.

*Documentation:
To copy subtree click on icon of node in content tree menu and choose <Copy Subtree>.
Then using browse mode choose parent node of new location of subtree being copied.
The size of subtree being copied are limited by MaxNodesCopySubtree. That is
implemented to avoid browser timeouts which can occur when you are trying to copy
big subtree. You can use copy subtree script (see bin/php/ezsubtreecopy.php,
doc/eng-us/features/subtree_copy_script.txt) instead of admin interface copy subtree
feature to get free of any limits (of course if you have proper admin rights to
run scripts on your site).

*Settings:
The settings for Copy Subtree feature are placed in file content.ini file, within
section [CopySettings]:
 MaxNodesCopySubtree   - Maximum allowable number of nodes to copy using Copy
                         Subtree feature (default 30).
 VersionHandling       - Use either user-defined, last-published or all
 CreatorHandling       - Sets current user as creators of copied contentobjects or
                         leave creators unchanged. Default 'current', use either
                         'user-defined', 'keep-unchanged' or 'current'. In the case
                         of 'user-defined', user will be prompt to choose how to
                         proceed this option during copying process.
 TimeHandling          - Save time of creation of objects being copied unchange or
                         sets new (current) time. Default 'current', use either
                         'user-defined', 'keep-unchanged' or 'current'. In the case
                         of 'user-defined', user will be prompt to choose how to
                         proceed this option during copying process.
 ShowCopySubtreeNotification
                       - Show or not notification after copying subtree (default
                         'enabled', use either 'enabled' or 'disabled'). On the
                         notification page you can see information about count of
                         copied nodes and errors happened during copying process.

*Modules:
kernel/content/copysubtree.php

*Templates:
templates/content/copy_subtree.tpl
templates/content/copy_subtree_notification.tpl