Fix Duplicate Badges

BadgeServiceImpl#saveNewBadgesFromIssueList filters already issued
badges by an incorrect key resulting in issuing the same badge for each
data retrieval cycle.

Author: systemtrap

sonar-connector/src/main/java/com/thepracticaldeveloper/devgame/modules/badges/calculators/UnitTesterBronzeBadgeCalculator.java

@@ -22,7 +22,7 @@ public class UnitTesterBronzeBadgeCalculator implements BadgeCalculator {
 
     @Override
     public String badgeKey() {
-        return "UT_BRONZE";
+        return KEY;
     }
 
     @Override

sonar-connector/src/main/java/com/thepracticaldeveloper/devgame/modules/badges/calculators/UnitTesterGoldBadgeCalculator.java

@@ -22,7 +22,7 @@ public class UnitTesterGoldBadgeCalculator implements BadgeCalculator {
 
     @Override
     public String badgeKey() {
-        return "UT_GOLD";
+        return KEY;
     }
 
     @Override

sonar-connector/src/main/java/com/thepracticaldeveloper/devgame/modules/badges/calculators/UnitTesterPaperBadgeCalculator.java

@@ -22,7 +22,7 @@ public class UnitTesterPaperBadgeCalculator implements BadgeCalculator {
 
     @Override
     public String badgeKey() {
-        return "UT_PAPER";
+        return KEY;
     }
 
     @Override

sonar-connector/src/main/java/com/thepracticaldeveloper/devgame/modules/badges/calculators/UnitTesterSilverBadgeCalculator.java

@@ -22,7 +22,7 @@ public class UnitTesterSilverBadgeCalculator implements BadgeCalculator {
 
     @Override
     public String badgeKey() {
-        return "UT_SILVER";
+        return KEY;
     }
 
     @Override