Dependency on ggCustomTJ

[TheoGervais]

Trying to install the vngMoM package from a blank session, with remotes::install_github('nimwegenLab/vngMoM') results in a failure due to the dependency of vngMoM to ggCustomTJ.
This comes from plot.faceted.tracks.R, line 138, where the periodic scale from ggCustomTJ is used. I am not sure it is intended. If so, I think it would be meaningful to update the readme with the information and how to install ggCustomTJ.
I did not update anything myself beause I am unsure whether this is relevant or not.