..F....... [ZBXNEXT-1583] Unify functionality of srctbl=prototype and srctbl=item_prototype - change to "item_prototype", remove traces of "prototype" usage. Improve code readability, use strict string comparison for srctbl on "item_prototype" and "graph_prototype". Fix minimum user level for graph prototypes and item prototypes to USER_TYPE_ZABBIX_ADMIN.