support for an optical device by fs.com

Attached changes add support for the FMT04-CH1U optical device, which can accommodate a number of optical modules (this patch adds support for fibre amplifier and an optical-electrical-optical convertor). The MIBs and the SNMP agent supplied with the device require a layer of index translation and use of get instead of walk.

I have tested the two attached patches (one for CE-17.9.0 and the other for 18.1.9002) and confirmed they both work as expected. You can see the sensors processed by poller.php in an attached file. Let me know if you need any additional information to merge these changes.