qwebchannel.js should be distributed properly

Currently the file is found in 2 places. Under markdown editor example in WebEngine examples and under WebChannel examples. When a user is trying to figure out where to find the file, they try to search Qt installation and see these two files. However, those files are not even identical and looks like the other has some bugfix applied that the other does not.

This should have a proper place where a user can easily find it and it should also be documented where to find it. Perhaps it could even have a separate download.