Clean up pan-genome tab axis labels

[shihabdider]

Describe the bug
Axis labels contain weird artifacts:

1. 0.5 seems to be rendered as 500m
2. There are negative axis values, but the min should be 0
3. Tick values should be whole numbers for the copy number axes across all plots, not floats
4. Tick values should not overlap the plot

[xanthopoulakis]

@shihabdider , can you please take a look if this is something that matches your expectation?

[shihabdider]

Reopening this with a new, related issue: right axis labels overlap with plot (this is irrespective of monitor size, it happens even on large monitors):

[xanthopoulakis]

This is a difficult one to tackle, do know it could take a while.