[FEATURE] Add dll registry extension point.

[rrahn]

Adds a dll registry to the GKN, which registers dlls shared between many generic nodes in a global registry. It also adds the SeqAn executor which overrides the setup of the execution environment to inject into the path environment the paths to the identified dlls.

I will test this on a windows machine first. Still you can review it already but wait for merging until I can confirm that it works on windows platforms.

[AlexanderFillbrunn]

I would change the extension point name to DLLProvider, as this is what people register in their plugins.

[rrahn]

@AlexanderFillbrunn it seems to work now on windows. 👍