x axis labels

[sinarueeger]

Add x axis labels to mhtplot. Instead of the continuum of 1:n, it should be 1:22, each in the middle of the chromosome

## create labels x axis
med.dat <- data %>% group_by(CHR) %>% summarise(median.x = median(cumsum.tmp))
data <- data %>% right_join(med.dat)
scale_x_continuous(breaks = med.dat$median.x, labels = med.dat$CHR)                     

This is how it looks currently (in fact without colors)

This is how it should look: