Fix merging of remote branches (#3096)

You can now 'clone' a remote repository and 'push' to it. There is no 'pull'
functionality because this can fail badly, so there is a 'fetch' which
retrieves all remote branches without merging (and never fails). The
user can then select the remote branch in the branch pull-down and merge
it.

src/blenderbim/blenderbim/tool/ifcgit.py

@@ -191,6 +191,13 @@ class IfcGit:
                 result[branch.commit.hexsha].append(branch)
             else:
                 result[branch.commit.hexsha] = [branch]
+        if repo.remotes:
+            for remote in repo.remotes:
+                for ref in remote.refs:
+                    if ref.commit.hexsha in result:
+                        result[ref.commit.hexsha].append(ref)
+                    else:
+                        result[ref.commit.hexsha] = [ref]
         return result
 
     @classmethod