Handle login timeouts

[robertvazan]

When not editing for a while, the next edit via WikibaseDataEditor fails due to session timeout. See the exception below. WDTK never recovers. Recovery has to be implemented on application level. It would be better if WDTK detected this kind of error, flagged the connection as disconnected, and automatically retried logging in on next request. Even better, it could retry the request that failed because of this.

org.wikidata.wdtk.wikibaseapi.apierrors.AssertUserFailedException: [assertuserfailed] You are no longer logged in, so the action could not be completed.
	at org.wikidata.wdtk.wikibaseapi.apierrors.MediaWikiApiErrorHandler.throwMediaWikiApiErrorException(MediaWikiApiErrorHandler.java:64)
	at org.wikidata.wdtk.wikibaseapi.ApiConnection.checkErrors(ApiConnection.java:438)
	at org.wikidata.wdtk.wikibaseapi.ApiConnection.sendJsonRequest(ApiConnection.java:366)
	at org.wikidata.wdtk.wikibaseapi.WbEditingAction.performAPIAction(WbEditingAction.java:747)
	at org.wikidata.wdtk.wikibaseapi.WbEditingAction.wbEditEntity(WbEditingAction.java:308)
	at org.wikidata.wdtk.wikibaseapi.WikibaseDataEditor.editEntityDocument(WikibaseDataEditor.java:628)