HST PageComposer incompatible with gson 2.2.3 - Backport to 7.8

In our project we need the following dependency for the integration with elastic search in the site pom:
<dependency>
<groupId>io.searchbox</groupId>
<artifactId>jest</artifactId>
<version>0.0.5</version>
</dependency>
This dependency however has a dependency on version 2.2.3 of com.google.code.gson:gson, which causes a problem when a draggable component is put in another container in the channel manager. This causes a reload, of the reload if the same action is repeated the component can be moved.

The problem is caused because the lastModifiedTimestamp is set in both org.hippoecm.hst.pagecomposer.jaxrs.model.ContainerRepresentation, and it's superclass org.hippoecm.hst.pagecomposer.jaxrs.model.ComponentRepresentation. Apparently gson 1.4 has no problem with this, but in 2.2.3 this is causing an exception.

There are a few possible solutions:
Make the Containerrepresentation use a proper (or no) superclass, it seems kind of stange that the ContainerRepresentation is a ComponentRepresentation.
Another solution would be to write the lastModifiedTimestamp in the ContanerRepresentation by using the setLastModifiedTimestamp method.
Fixing this bug will improve the integration with elastic search in general.