simple copy@paste
- copies one node
- copies a selection. When copying a selection it also duplicates the edges that are contained in the selection

Only works withing the same document due to Clipboard browser restriction
- scoped the Clipboard like the other .js files
- duplicate nodes also on Copy (duplicate twice) so we support also Cut & Paste
Merge branch 'pr/167' into dev
refactor clipboard a little bit #167

* cloneObject helper function
* don’t need makeNewId outside of this scope
* cloning the whole node/edge makes copy a little more future-proof
2 space #167
handle addressable port(s) on paste #167
proper array `for` loops #167