r4016 Merging Jens Weibler SNMPv3 patch to be tested on real hardware.

r4016 Merging Jens Weibler SNMPv3 patch to be tested on real hardware.

querySNMPData(): detect protocol version
renderSNMPPortFinder(): extend the FORM for more INPUTs
SNMP: new abstract class
SNMPv2: new protocol implementation class
SNMPv3: ditto
SNMPDevice: employ SNMPv2/SNMPv3 classes, add get/set methods
doSNMPmining(): make use of SNMPDevice class
doSwitchSNMPmining(): idem
doPDUSNMPmining(): idem
APCPowerSwitch: use snmpset/snmpget methods instead of library functions