Replace application icon to proper

[Andersen27]

Old path to application icon ("Assets/electron.ico") did not work. The Electron default icon was displayed, which can be seen when changing the icon file to another. The following path is correct: "bin/Assets/electron.ico". But in order for the developers to see that the custom icon definition really works, I replaced the icon with the one located in wwwroot. So the "ElectronNET-API-Demos/Assets/" folder is no longer needed and has been deleted.

Also BrowserWindow's icon was defined relative to OS platform (edits inside electron.manifest.json is enough for Windows, but this is a working example that can be useful to developers, specifically for Linux).

P.S: Refreshing the icon cache (Windows)