Add label field to task definition

Label is an alternative name for task that replace it when printed in following context eg.:

- log: when given task is up to date and is skipped from execution
- log: when given task is NOT up to date (`--status` command)
- in `--summary` and `--list` commands output

variables.go

@@ -32,6 +32,7 @@ func (e *Executor) CompiledTask(call taskfile.Call) (*taskfile.Task, error) {
 
 	new := taskfile.Task{
 		Task:        origTask.Task,
+		Label:       r.Replace(origTask.Label),
 		Desc:        r.Replace(origTask.Desc),
 		Summary:     r.Replace(origTask.Summary),
 		Sources:     r.ReplaceSlice(origTask.Sources),