Navis

Added MANC (male adult nerve cord) dataset:
- template (including meshes) for `MANC` (nm) and `MANCraw` (voxel)
- added download for `JRCVNC2018M` <-> `MANC`

- adds a transform between the male CNS and FlyWire
- adds `_navis_units` properties to the template meta data

This fixes an error in the URL used to download the JRC2018U to JRC2018M transform that led to the wrong transform being downloaded.

Added a (downloadable) JRC2018U <-> JRC2018M.

This fixes a critical error with a wrong filename (not sure how that slipped past tbh).

We also add a preliminary transform for FAFB <-> JRCFIB2022M (male CNS) and a JRCFIB2022M neuropil mesh.

This version adds a template and a mirror transform for `FLYWIRE`. In addition, `FAFB` is now a full synonym for `FAFB14`.