Added service method tests + javadocs

restservice/src/main/java/com/plannaplan/controllers/GroupController.java

@@ -41,7 +41,7 @@ public class GroupController {
             @RequestParam(name = "capacity", defaultValue = "true") @ApiParam(value = "Boolean if we want to have capacity field in response") Boolean capacity,
             @RequestParam(name = "takenPlaces", defaultValue = "false") @ApiParam(value = "Boolean if we want to have respoonse with information about taken places by other students") Boolean takenPlaces) {
         List<Groups> groups = this.groupService.getGroupsByCourse(id);
-        HashMap<Groups, Integer> ammounts;
+        HashMap<Long, Integer> ammounts;
 
         if (takenPlaces) {
             ammounts = this.groupService.getTakenPlaces(groups);