add optimistic rendering for staging and unstaging files

pkg/gui/filetree/file_tree.go

@@ -41,6 +41,7 @@ type IFileTree interface {
 	GetAllItems() []*FileNode
 	GetAllFiles() []*models.File
 	GetFilter() FileTreeDisplayFilter
+	GetRoot() *FileNode
 }
 
 type FileTree struct {
@@ -159,6 +160,10 @@ func (self *FileTree) Tree() INode {
 	return self.tree
 }
 
+func (self *FileTree) GetRoot() *FileNode {
+	return self.tree
+}
+
 func (self *FileTree) CollapsedPaths() *CollapsedPaths {
 	return self.collapsedPaths
 }