Merge GlobalScopes into a single scope

[luczsoma]

After merging imports and exports, we should have one global scope for a project with the child scopes connected. Now we have one GlobalScope for each imported file.

[steindani]

What would we gain from this? I was thinking about it for a while, but dismissed the idea, since the scope of the modules are not merged, only references are imported. Maybe global variables should be extracted, like window.