CRM-15578 - crmMailing2 - Implement multiple sections

Highlights of changes:
 * Implement "Message Template" options. Add crmUiSelect.
 * Implement "Schedule" pane. Add crmUiDate, crmUiTime, and crmUiDateTime.
 * Implement "Review" pane.
 * Change table-based layout to divs. Change crmUiLabel to crmUiField.