Improve drag and drop onto palette with automatic wiring support

Idea:
When dropping a figure on another (for instance a log onto a timer) then this will connect these two figures automatically if allowed. If timer already is connected to another figure (lets say bean) then it automatically inserts the log between the timer and the bean doing all needed rewiring. We need to check in those cases if the final wiring state would be allowed or not before actually allowing the drop.

The insert could also be done / or additionally by dropping a figure on a connection.

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How it works now:
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This feature makes it possible to drop a figure on the diagram and automatically get it wired to other nodes. The current solution supports 2 modes:

Append:
You can now drop new nodes from the palette onto a node in the diagram (lets call that node drop target). If the drop target has an outgoing connection to another node you are not allowed to drop the new node. If the drop target has no outgoing connection the new node will be placed behind the drop target and then automatically connect drop target to new node.

Insert:
This mode only works on connections between diagram figures. If you drop a new node onto a connection then it will be inserted between the two nodes connected by this connection. Example: you have a file poller connected to a file writer. You drop a log endpoint on the connection between these 2 figures. The new flow looks like this: File Poller --> Log --> File Writer.