[Example] Limit telemetry responses to 5000 records

Update example telemetry providers to limit the number of
datums generated so that queries for long time ranges will
not cause undesired behavior in demos.

example/imagery/plugin.js

@@ -79,7 +79,7 @@ define([
                 var start = options.start;
                 var end = options.end;
                 var data = [];
-                while (start < end) {
+                while (start < end && data.length < 5000) {
                     data.push(pointForTimestamp(start));
                     start += 5000;
                 }