Both on the backend (replaced with DEFAULT view) and on the front end (removing UI menu items).

Includes removing an if-statement that should've been dead but was erronously applied to the following statement. Dead code = bad, if-statements without braces = bad.

Without this, when you go to airframe config and the current config is
Simulation it will not be selected. Hence you won’t know what the
current config is.

I don't think it's needed anywhere in QGC since this has been a bug for a long time.

SLUGS has maintained their patches out-of-tree for a long while now.
These will eventually get merged back in, but it'll be easier to evaluate them as fresh commits instead of modifications to this old & dead code, so we'll delete this for now.

Some functionality was lost, will need to be fixed in a later commit.

To include OpenGL primitives, we include the QtOpenGL header instead, which has all the platform-specific includes taken care of for us.

Also added selection from tree view for downloading