Split Zabbix Agent, SNMP and External check timeouts

Just leaving this here. If at all possible it would be nice to seperate the timeouts for:

• Agent
• SNMP 
• Externalcheck

Right now they are all the same setting:

### Option: Timeout
#       Specifies how long we wait for agent, SNMP device or external check (in seconds).
#
# Mandatory: no
# Range: 1-30
# Default:
# Timeout=3

This way, if we have slow external checks we don't need to increase Agent and SNMP as well.