Add possibility to change project from the editor.

[sicher]

The only way currently to switch project is to quit and relaunch.

Add either an "Open Project" if the project browser works when the editor is running, or "Close Project" that takes the user back to the project launcher.

[supersaiyansubtlety]

Any progress? This seems like a very simple but very useful feature to add.

[markusgustavssonking]

Related: #303

[lutalli]

+1! And it's more than 3 years. I think this feature would bring much convenience.