[FEATURE REQUEST] Make org-copy-subtree and org-cut-subtree work on an active region

[Philipp Kiefer]

When calling either org-copy-subtree or org-cut-subtree, check if there 
is an active region that starts on a headline and contains at least one 
more headline of the same level. If so, copy / cut all the subtrees 
touched by the region. This saves the user having to count the subtrees 
he / she wants to operate on in order to use the number as a prefix 
argument for the command. This change  would make the process easier and 
provide visual feedback.

Optionally require that the active region fully encloses two or more 
headlines and nothing else, i. e. that it begins at the start of one 
headline and terminates at the end of another headline.

Thanks.