Node Editor Plugin Library

[Schneegans]

This PR adds a new plugin library: csl-node-editor. With this library, plugins can provide a user interface for creating complex data flow graph. The node editor interface is made available via a web server. Hence the node graph can be modified either within CosmoScout VR or on an external device.

It also adds a new plugin: csp-demo-node-editor. This serves as an example on how to use the csl-node-editor plugin library for creating data flow graphs within CosmoScout VR. To enable this plugin, add this to your config:

{
  ...
  "plugins": {
    ...
    "csp-demo-node-editor": {
        "port": 9999
    }
  }
}

[coveralls]

Pull Request Test Coverage Report for Build 3513209761

• 0 of 427 (0.0%) changed or added relevant lines in 20 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage decreased (-0.08%) to 2.934%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
plugins/csl-node-editor/src/internal/CommunicationChannel.hpp	0	1	0.0%
plugins/csl-node-editor/src/internal/NodeGraph.hpp	0	1	0.0%
plugins/csp-demo-node-editor/src/nodes/DisplayNode.hpp	0	1	0.0%
plugins/csp-demo-node-editor/src/nodes/MathNode.hpp	0	1	0.0%
plugins/csp-demo-node-editor/src/nodes/NumberNode.hpp	0	1	0.0%
plugins/csl-node-editor/src/internal/NodeConnection.hpp	0	2	0.0%
plugins/csl-node-editor/src/logger.cpp	0	3	0.0%
plugins/csp-demo-node-editor/src/logger.cpp	0	3	0.0%
plugins/csl-node-editor/src/NodeFactory.hpp	0	4	0.0%
plugins/csp-demo-node-editor/src/nodes/DisplayNode.cpp	0	11	0.0%
<!--	Total:	0	427	0.0%	-->

Totals
Change from base Build 3367995061:	-0.08%
Covered Lines:	491
Relevant Lines:	16734

---

💛 - Coveralls

[Schneegans]

Fuah, this was a lot. Thank you very much for the thorough review. I think I handled all requested changes...

Let's see what we can build with this!