Add copy/paste functionality between model tabs

[deinhofer]

The WebACS supports editing several model files in seperate tabs (see pic). It would be very handy to if model contents could be copied from one model to another with typical shortcuts and mouse actions.

[kingcole]

that's why this functionality exists already --> try CRTL-C / CTRL-V on different tabs;
alternatively you can use the buttons in the Edit-Tab

[deinhofer]

I have just tested it on the following browsers, OSs:

• firefox 58.02, Win 7: OK
• chrome 63, Win 7: Not working