extentending snmp_sync support for Juniper

I've extended the dictionary/snmp.php with all Juniper devices currently supported by the juniper-mibs. Because all Junos based devices are using pics as module for interfaces, I've written a function to parse the pic string and add the corresponding interfaces. This works also with EX virtual chassis (switch-stacks) and SRX-cluster (firewall-cluster).

I've tested with different devices from EX, MX and SRX series including stacks and cluster.