Adds ability to generate graphs for custom areas

This commit adds the ability to generate individual PNG and SVG graphs
for custom areas, defined as the union of several "Àrees Bàsiques de
Salut" (ABS) in the config/customAreas.php file.

Change-Id: I27f34b4a8f520a38c55eed224554b470c5ba2938
diff --git a/cron/includes/plotCustomGraph.gnu b/cron/includes/plotCustomGraph.gnu
new file mode 100644
index 0000000..acf66aa
--- /dev/null
+++ b/cron/includes/plotCustomGraph.gnu
@@ -0,0 +1,19 @@
+set xlabel "Casos actius per 10^5 habitants"
+set ylabel "Mitjana taxa de creixement darrers 7 dies"
+set title font "Helvetica,20"
+set yrange[0:5]
+set xrange[0:800]
+set samples 400
+set key off
+set tics out scale 0.5,0.2
+min(a, b) = (a < b ? a : b)
+# The different colored areas correspond to the classification of the EPG values defined on page 8 at
+lastUpdated = system("tail -n 1 ".fileName." | awk '{print $1;}'")
+graphTitle = name
+graphDataFile = fileName
+load "includes/plotSingleGraph.gnu"