Refactor, optimization, bugfixes

Hding sensitive information in the logs (like Zabbix usernames and passwords).
Only requiring 2 Zabbix values (event.id, item.id) to be passed (other information is picked up from Zabbix).
Refactoring and optimization of the code (logic change and ensuring least possible amount of calls and information sets required).
Some bug fixes (mainly surfaced after the refactoring).
Revised/optimized template logic (allow passing and processing of dynamic list of graphs).