Revert "Remove 50% option"

This reverts commit 372d15578f.

ts/routes/graphs/PercentageRange.svelte

@@ -11,6 +11,14 @@ License: GNU AGPL, version 3 or later; http://www.gnu.org/licenses/agpl.html
 </script>
 
 <InputBox>
+    <label>
+        <input
+            type="radio"
+            bind:group={range}
+            value={PercentageRangeEnum.Percentile50}
+        />
+        50%
+    </label>
     <label>
         <input
             type="radio"

ts/routes/graphs/percentageRange.ts

@@ -7,12 +7,15 @@ export enum PercentageRangeEnum {
     All = 0,
     Percentile100 = 1,
     Percentile95 = 2,
+    Percentile50 = 3,
 }
 
 export function PercentageRangeToQuantile(range: PercentageRangeEnum) {
+    // These are halved because the quantiles are in both directions
     return ({
         [PercentageRangeEnum.Percentile100]: 1,
-        [PercentageRangeEnum.Percentile95]: 0.975, // this is halved because the quantiles are in both directions
+        [PercentageRangeEnum.Percentile95]: 0.975,
+        [PercentageRangeEnum.Percentile50]: 0.75,
         [PercentageRangeEnum.All]: undefined,
     })[range];
 }