Offer to migrate local context to global context when creation of global context lead to conflict

[ptitFicus]

1. Create a project "foo"
2. Create a local context / subcontext
3. Create the same global context / subcontext <- this results in an error explaining the conflict

There is currently no easy way to solve this situation, a nice thing would be a popup offering to migrate the local context in a global one. This would imply to make the change for associated overload an subcontexts.