plot_timeline_ggplot aesthetics, highlight marker genes.

[moi-taiga]

It would be nice to have the default for gene names/points be black and colour user-selected genes in red.

[moi-taiga]

also:

Warning messages:
1: Using size aesthetic for lines was deprecated in ggplot2 3.4.0.
i Please use linewidth instead.
i The deprecated feature was likely used in the GeneSwitches package.
Please report the issue to the authors.