Add abillity to paste children to many samplers at once

**pozostalerzeczy** ([Bug 63449](https://bz.apache.org/bugzilla//show_bug.cgi?id=63449&redirect=false)):
Hi,
Imagine a following scenario:
I have N samplers, with assertions relying on error messages, which in turn are generated based on data retrieved by a JDBC preprocessor, the thread group structure is :

Sampler
-JDBC preprocessor (fetch data)
-JSR223 preprocessor (generate error message)
-JSR223 assertion (check if sampler returned correct error message)

As there are many samplers in that thread group, it's quite tiresome to copy those three children elements from first created sampler, and then have to select and paste to each individual sampler.

Would it be possible for the paste-children operation to affect all selected samplers? (Eg. selected using Shift+arrows combination).

OS: All