Rationale and Design of a Clinical Trial to Evaluate the Safety and Efficacy of Intracoronary Infusion of Allogeneic Human Cardiac Stem Cells in Patients with Acute Myocardial Infarction and Left Ventricular Dysfunction: The Randomized Multicenter Double-Blind Controlled CAREMI Trial (Cardiac Stem Cells in Patients with Acute Myocardial Infarction)