include additional ISSNs in the journals route

the journals route doesn't currently use/store additional ISSNs - can we add those? all the better if we previous ISSN(s) can be specified

[jenniferlin15]

from internal discussion thread:
once the p-issn and the e-issn of a journal are defined, any other ISSNS that are added to the journal become "additional issns". The additional ISSNS for the journals route can be added though, it's in the file that's being used to generate the journals data.