* VuFind/Search/Solr/AbstractErrorListener.php (attach): New
  method. Attach to shared event manager.

* VuFind/Search/Solr/V3/ErrorListener.php: Extend
  AbstractErrorListener.
* VuFind/Search/Solr/V4/ErrorListener.php: Extend
  AbstractErrorListener.
* VuFind/Search/Solr/AbstractErrorListener.php: New
  class. Abstract base class of error listeners.

* VuFind/Search/Solr/V4/ErrorListener.php
  (getResponseBodyMediaType): New function. Return normalized
  response body media type identifier.
  (analyzeJsonErrorResponse): New function. Analyze response body
  and return appropriate tags.
  (onSearchError): Refactored. Use new functions.

Thanks to Ere Maijala and Chris Hallberg.

Thanks to Michele Meloni.

Thanks to Michele Meloni.

* VuFindSearch/Backend/Summon/Backend.php (search, retrieve):
  Catch Summon Exception and rethrow as BackendException.

Resolves VUFIND-749.

Same problem as before with title
Value not set for new record

MyResearch/EditList/NEW?recordId=xxxxx&recordSource=VuFind
Caused an error because title is not set in list object

* VuFind/Search/Solr/V3/ErrorListener.php: Check for
  HttpErrorException instead of BackendException.

* VuFindSearch/Backend/SRU/Connector.php (checkForHttpError): Dto.
* VuFindSearch/Backend/Solr/Connector.php (send): Use
  HttpErrorException instead of BackendException.
* VuFindSearch/Backend/Exception/HttpErrorException.php: New
  class. Base class of HTTP error exceptions.
* VuFindSearch/Backend/Exception/HttpErrorException.php
  ($response, __construct, getResponse, createFromResponse): Moved
  to HttpErrorException.

* VuFindSearch/Backend/SRU/Connector.php (process): Throw
  BackendException on XSLT processing error, don't check for XML
  prolog.

* VuFindSearch/Backend/SRU/Connector.php (process): Throw
  BackendException instead of generic Exception.
  (checkForHttpError): Use BackendException factory.

* VuFindSearch/Backend/Exception/BackendException.php (static): Prefix
  reason phrase with status code.

* VuFindSearch/Backend/Solr/Connector.php (send): Use exception
  factory.
* VuFindSearch/Backend/Exception/BackendException.php
  (createFromResponse): New function. Create exception based on
  server response.