added some utility methods to bot service

reworked message cache to not be jda messages, but own objects: cachedMessages, jda messages should not be kept around
added listener to listen for message links, to represent them in an embed (or embeds)
added offsetDateTime handling for gson
introduced a way on how to handle async transaction handling for suggestions and message loading (self reference with another method with transactional)
added timestamp support to embeds

abstracto-application/core/core-impl/pom.xml

@@ -98,6 +98,11 @@
             <artifactId>caffeine</artifactId>
         </dependency>
 
+        <dependency>
+            <groupId>com.google.code.gson</groupId>
+            <artifactId>gson</artifactId>
+        </dependency>
+
     </dependencies>
 
 </project>