Submodule improvements

Hi, we use GitExtensions and sub-modules intensively and we have missed some small features to make it less confusing and error prone. The pull request is associated with the issue https://github.com/gitextensions/gitextensions/issues/2161

I've implemented them starting from the last tag (2.47.3) because I was having problems to run master, but I could do the merge to master. Don't know who typically does that on a pull request. 

I'll explain the changes on each commit.