Implemented Buisnesslogic to read and save correct polling configuration

- added min and max values to config files
- updated ControllerPollProperties: added getter and setter of min and max values
- updated PollConfigurationHelper: added getter for different values

Signed-off-by: Nonnenmacher Fabian <fabian.nonnenmacher@bosch-si.com>

hawkbit-core/src/main/java/org/eclipse/hawkbit/ControllerPollProperties.java

@@ -20,6 +20,8 @@ public class ControllerPollProperties {
 
     private String pollingTime = "00:05:00";
     private String pollingOverdueTime = "00:05:00";
+    private String maxPollingTime = "23:59:00";
+    private String minPollingTime = "23:59:00";
 
     public String getPollingTime() {
         return pollingTime;
@@ -36,4 +38,20 @@ public class ControllerPollProperties {
     public void setPollingOverdueTime(final String pollingOverdue) {
         this.pollingOverdueTime = pollingOverdue;
     }
+
+    public String getMaxPollingTime() {
+        return maxPollingTime;
+    }
+
+    public void setMaxPollingTime(String maxPollingTime) {
+        this.maxPollingTime = maxPollingTime;
+    }
+
+    public String getMinPollingTime() {
+        return minPollingTime;
+    }
+
+    public void setMinPollingTime(String minPollingTime) {
+        this.minPollingTime = minPollingTime;
+    }
 }