Multiple levelplots with title and subtitle in R

I had quite a fight with R to put multiple levelplots with a shared title and subtite on the same chart, so I thought I put a PoC code here:

library(lattice)
m <- matrix(c(0.1,0.2,0.3,0.4), 2, 2)
col.l <- colorRampPalette(c('blue', 'green'))(30)

plot.new()
par(mfrow=c(2,2), oma=c(2,0,2,0))
print(levelplot(m, col.regions=col.l, main="L1"), split=c(1, 1, 2, 2)) 
print(levelplot(m, col.regions=col.l, main="L2"), split=c(1, 2, 2, 2), newpage=FALSE)
print(levelplot(m, col.regions=col.l, main="L3"), split=c(2, 1, 2, 2), newpage=FALSE)
print(levelplot(m, col.regions=col.l, main="L4"), split=c(2, 2, 2, 2), newpage=FALSE)
title("Centered Overall Title", outer=TRUE)
mtext(side=1, "Centered Subtitle", outer=TRUE)

The result should be something similar like this:

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