put the module_include "customer_list_header" in the correct place

In the templates customers, this module include was called before the firstname in the THEAD
whereas the module_include "customer_list_row" is called after the column Lastname
=> wrong order

Adding the module_include "customer_list_header" in the search.html template in the THEAD because there is the module_include "customer_list_row" in the TBODY