How to add axis labels?

[vertesy]

Related to #15, this is a feature request.

I would like to add axis label, in addition to column labels, as possible with heatmaply:
This is a gllobal X and Y label as in usual plots.

I tried

• labs()
• ggtitle
• annotate()
• geom_text()

e.g:

>   ggheatmap::ggheatmap(data_matrix ) + labs(title = 'title', subtitle = 'subtitle', caption = 'caption')
# plot is generated, and labeled correctly

>   ggheatmap::ggheatmap(data_matrix ) + labs(title = 'title', subtitle = 'subtitle', caption = 'caption', x ="111", y ="1212121")
# no x y labels added 

Otherwise labs() works

 p <- ggplot(mtcars, aes(mpg, wt, colour = cyl)) + geom_point()
 p + labs(x = "New x label")

Also nothing (may have mistakes):

 p + 
  geom_text(label="Custom X Label", x=5, y=0, hjust=1, vjust=1, size=5) +
  geom_text(label="Custom Y Label", x=0, y=35, angle=90, hjust=1, vjust=1, size=5)

Same for other trials