Add graph class and extend liveGraph from graph

docs/brainstorm/SoftwareDocumentatie/graph_classes.md

@@ -14,11 +14,21 @@ The graphs are used to display the data from the sensors. The data is collected
 
 ## Class diagrams
 
+### Graphs
+
+```mermaid
+classDiagram
+    class graph {
+        +nodeId
+        makeGraph()
+    }
+```
+
 ### Live graphs
 
 ```mermaid
 classDiagram
-    class liveGraph {
+    class liveGraph extends graph {
         +nodeId
         +cnt
         +timeArray