create utils.getGraphType() function.

also apply setting to long term graphs
flip logic - only return "line" if the setting is explicitly set to "false"

Signed-off-by: Adam Warner <me@adamwarner.co.uk>

scripts/pi-hole/js/db_graph.js

@@ -151,7 +151,7 @@ $(function () {
   var blockedColor = "#999";
   var permittedColor = "#00a65a";
   timeLineChart = new Chart(ctx, {
-    type: "bar",
+    type: utils.getGraphType(),
     data: {
       labels: [],
       datasets: [