Remove implicit project admin rights for programme admins

[somathias]

Currently programme admins are automatically given the rights to add and remove members to any project under the programme they administer without them explicitly being project admins as well.

This functionality should be removed, ie. only users listed explicitly as project admins should have project admin rights. If a programme admin needs project admin rights they should set themselves as project admins on the project.

When implementing this change, it needs to be made sure that projects cannot be orphaned, ie. left without any project admin.

Update documentation when done.

[floradanna]

@wittigue @smza this is something we might want to discuss at our community workers meeting