Rework handling of serverInstallablePlugins

[GiantTreeLP]

Currently plugins which can be hosted on the wrapper, the master or any network resource are loaded rather crudely with a lot of smelly, duplicated and error-prone code.

This issue is a marker for the project and acts as a hub for discussion about this feature.

Any changes to the current implementation of serverInstallablePlugins should not result in any change to the configuration or overarching API.

[TheMeinerLP]

The plan was to remove in the future the feature or rework with all of the template system.

[GiantTreeLP]

This can be thought of an intermediate step to improve code quality so that later we can pull in the good code.
Maybe you can incorporate this into #248

[TheMeinerLP]

I can do this, but i make that in a extra pull request. That's the better way