Add support for synonym search to vfb_tovfbids

[jefferis]

Still needs to check with @Robbie1977 if this selection of fields makes sense

[jefferis]

Doesn't work for VT ids unfortunately:

> vfb_tovfbids('VT017929')
[1] NA
> vfb_tovfbids('VT017929', synonyms = F)
[1] NA
> vfb_tovfbids('VT017929', synonyms = F, fixed=T)
[1] NA
> vfb_tovfbids('VT017929', synonyms = F, fixed=F)
character(0)
> vfb_tovfbids('VT017929*', synonyms = F, fixed=F)
[1] "VFB_00064845" "VFB_00064844"
> vfb_tovfbids('VT017929*', synonyms = T, fixed=F)
character(0)

[jefferis]

@Robbie1977 while you are here, do you know what I would need to do to get VT-GAL4 id search working?