[mod] oscar: /preferences , engines tab: report engine times

* display the median time instead of the average.
* add a "Reliability" column (sum up the metrics and the checker results).
* the "selected language", "SafeSearch", "Time range" values are displayed as "broken" when the checker tests fail.

searx/static/themes/oscar/src/less/logicodev/variables.less

@@ -14,3 +14,5 @@
 @light-green: #01D7D4;
 @orange: #FFA92F;
 @dark-red: #c9432f;
+
+@stacked-bar-chart: rgb(0, 0, 0);