Add "Unique Name" field to readout modules

[nkx111]

When the readout plane is large and contains many readout modules, the current implementation might be difficult to identify each. We have:

1. TRestDetectorReadoutModule::fModuleID to identify module id. It is an int number, may not be so clear to the users.
2. TRestDetectorReadoutModule::fModuleName to identify the module type, either 128 channel MicroMegas or pixel readout module.

So I suggest to add a new field fUniqueName to TRestDetectorReadoutModule class. It would be a string data member, and therefore be better to record module names or serial numbers. For example, "V2M2", "V6_05", "A1580HN.46", something like that.