Added menu "Management configuration" to Kconfig with:
-moved options from "Local Network Configuration":
 --SNMP_TRAPSINK_ADDRESS
 --SNMP_TRAP2SINK_ADDRESS
 --SNMP_RO_COMMUNITY
 --SNMP_RW_COMMUNITY
-added threshold levels:
 --SNMP_TEMP_THOLD_FPGA
 --SNMP_TEMP_THOLD_PLL
 --SNMP_TEMP_THOLD_PSL
 --SNMP_TEMP_THOLD_PSR

Update user manual.

Signed-off-by: Adam Wujek <adam.wujek@cern.ch>