Filtering C# projects in the standard version's project library.

[ottop]

When using the standard version of Godot, C# is not supported. However, the project library still shows C# projects, which end up not working.

This could be solved by tagging anything made with C# as such and hiding it by default on the standard edition of the game engine. Currently these clutter up the project library even though they cannot be used in the version of the game engine, which is kind of unintuitive.