In-app dialog for local and remote files

[willneedit]

Reaf. #111 and #113 it could be more convenient to manage the user data (like name, or uploading the 2D icons) or, maybe, a dedicated server's data.

For user data, the microserver would be localhost only - no remote connection. But, for server data, it would require remote connections, along with the website security and authentication.

[willneedit]

Maybe it's a little overblown. The in-app UI for configuration is enough, except for a file dialog to upload user data, like worlds, user icons and avatars.

A file dialog both needs navigating the local file system and the ability to just state a web URL.

[willneedit]

Title changed due to the limited scope of the task