snmp: remove unused variable
images: add an image for Juniper EX2200-48T
images: add an image for Juniper EX3300-48T
images: also provide Juniper EX*-24T images

However, since this is not possible to make a distinction just with
sysObjectID, we don't really use them.
misc: update lldpd and wiremaps homepages
datastore: strip out invalid characters by encoding to unicode