Moved formatting out of Category.java

src/main/java/cz/muni/fi/pv168/project/data/category/Category.java

 package cz.muni.fi.pv168.project.data.category;
 
 import cz.muni.fi.pv168.project.data.IdentifiableEntity;
-import cz.muni.fi.pv168.project.ui.i18n.I18N;
 
 import java.awt.*;
 import java.time.Duration;
@@ -12,8 +11,6 @@ import java.util.Objects;
 
 public class Category implements IdentifiableEntity {
 
-    private static final I18N I18N = new I18N(Category.class);
-
     private Long id;
     private String name;
     private Color color;
@@ -46,10 +43,6 @@ public class Category implements IdentifiableEntity {
         return this.name;
     }
 
-    public String getTimeDurationFormatted(LocalDate fromDate, LocalDate toDate) {
-        return getTotalDuration(fromDate, toDate).toHours() + " hours";
-    }
-
     public Duration getTotalDuration(LocalDate fromDate, LocalDate toDate) {
         return this.timeSpents
                 .stream()

src/main/java/cz/muni/fi/pv168/project/model/CategoryStatisticsTableModel.java

@@ -41,12 +41,16 @@ public class CategoryStatisticsTableModel extends AbstractTableModel implements
             case 0:
                 return category;
             case 1:
-                return category.getTimeDurationFormatted(fromDate, toDate);
+                return getTimeDurationFormatted(category);
             default:
                 throw new IndexOutOfBoundsException("Invalid column index: " + columnIndex);
         }
     }
 
+    public String getTimeDurationFormatted(Category category) {
+        return category.getTotalDuration(fromDate, toDate).toHours() + " hours";
+    }
+
     @Override
     public String getColumnName(int columnIndex) {
         switch (columnIndex) {

src/main/resources/cz/muni/fi/pv168/project/data/category/i18n.properties

-Category.timePeriodFormat={0,choice,0#|1#1 day|1<{0,number,integer} days} {1,choice,0#0 hours|1#1 hour|1<{1,number,integer} hours}

src/main/resources/cz/muni/fi/pv168/project/data/category/i18n_cs.properties

-Category.timePeriodFormat={0,choice,0#|1#1 den|1<{0,number,integer} dny|4<{0,number,integer} dn\u016F} \
-  {1,choice,0#0 hodin|1#1 hodina|1<{1,number,integer} hodiny|4<{1,number,integer} hodin}