Signpost window

[daemontus]

Signpost window is the "welcome" screen of AEON sketchbook.
It allows to:

• Create new sketch.
• Import network/sketch.
• Open some stand-alone data explorer (classification, state space, etc.).
• Lists previously opened projects.
• Allows to start a workflow.

This should be a relatively simple window with basically no state except for the previously opened projects. But we probably won't be able to finish this until all other features are at least working, so it's definitely not a priority. Maybe we can use it for some initial UI experiments.

[ondrej33]

A very basic version of the signpost page was added in #55. For now, the initial screen displays a "welcome" message, a logo, a few hints, and several buttons leading to the editor. Users can start a new project, load a model of any supported format, or load an example TLGL model. The signpost is part of the editor window and is conditionally rendered before any user action happens.

In future, we might make it a separate window, but it would be an overkill at the moment. We could also add the list of previously opened projects. There are no workflows yet since the current app only has inference.