[IT-2780] Remove null values before calculating percentile value

* TimeSeriesChart: Now with style 😎

* Card background
* Applied colors to axis
* Y-Axis ticks over complete with
* X-Axis labels with linebreaks

* TimeSeriesChart: Added y-axis description text

* TimeSeries: Added missing i18n text

* [IT-2780] Remove null values before calculating percentile value

src/main/groovy/de/iteratec/osm/result/dao/query/AggregationUtil.groovy

@@ -60,6 +60,7 @@ class AggregationUtil {
     }
 
     static def getPercentile(List<Number> data, int percentage) {
+        data = data.findAll {it != null}
         int index = (data.size() * (percentage.toFloat() / 100f)).toInteger()
         index = Math.min(data.size() - 1, Math.max(0, index))
         return getPercentileByIndex(data, index)