Are you sure this is all of the files? When I extract what you provided to the plugins folder this is the error message I get:
"Plugin “DialogueSystem” failed to load because module “DialogueSystem"could not be found. Please ensure the plugin is properly installed, otherwise consider disabling the plugin for this project”.
I tried dropping the plugin in while UE4 was open as well, and when I do that does pop up under the plugins windows in the project and allow me to enable it, but then it asks to restart. And again, if I restart the project I get the same above error when attempting to launch UE4. This is version 4.15 Im using btw, are you sure it works?