Summary

Closes: #144

• Processes can be exported in the Form of PNG files
• Processes can be copied from the modeler into the clipboard in the form of a PNG image

Details

• fixed the util functions in the bpmn-helper to also find participants (getChildren, getAllElements, getElementById,...)
• Pressing CTRL+C in the modeler copies a PNG (of the currently selected elements) of the process into the users clipboard that may be pasted into other programs
• The user can select to export processes as PNG images
• The PNG export has the options to also export referenced processes and collapsed subprocesses
• The PNG export has three "quality" options that will upscale the PNG image from the SVG with different factors (1.5 , 2.5, 4); the final upscaling might be smaller if the process diagram is too big to be exported with the selected amount of upscaling