Copy-and-paste support

[rsimon]

It would be nice to be able to copy an annotation (CTRL+C). Then, after having created a new selection, CTRL+V would insert all the bodies of the copied annotation into the new one.

(Note: this should actually possible to accomplish through a plugin, without the need to hack into the actual core codebase. And the process would be identical for RecogitoJS and Annotorious, which means it will work for both text & image annotation.)