* VuFindSearch/Backend/Solr/Connector.php (__construct):
  Initialize query invariants, defaults, and appends.
  (getQueryDefaults, getQueryAppends, setQueryDefaults)
  (setQueryAppends, addQueryDefault, addQueryAppend): Set, get, add
  to query defaults and appends.
(prepare): Compose final parameters.
* VuFind/Search/Factory/AbstractSolrBackendFactory.php
  (createConnector): Add parameters as query appends, initialize
  defaults.

* VuFindSearch/Backend/Solr/Connector.php (prepare): Return
  prepared params.
  (select, alphabeticBrowse, getTerms): Use return value.

* VuFindSearch/ParamBag.php (getArrayCopy): New function. Return
  parameters as array.

* VuFindSearch/Backend/Solr/Backend.php (update, deleteAll)
  (delete): Define methods to fullfill WritableBackendInterface.

* VuFindSearch/Backend/Feature/WritableBackendInterface.php (delete):
  New interface.
* VuFindSearch/Backend/BackendInterface.php (similar): Moved to
  Feature/WritableBackendInterface.

* VuFindSearch/Backend/Solr/Response/Json/Facets.php
  (getFieldFacets): Lazy-load field facet information.
  (getQueryFacets): New function. Return lazy-loaded query facet information.
  ($facets): New property. SOLR facet information.
  ($queries): New property. Query facets.

* VuFindSearch/Backend/Solr/Backend.php (__construct): Use null as
default backend identifier.

* VuFindSearch/Service.php: Only trigger pre and post events, listener
  must pick up operation from event params.

* VuFindSearch/Backend/Solr/Response/Json/RecordCollectionFactory.php
(__construct): Fix wrong comparism introduced for testing.

* VuFindSearch/Backend/Solr/Backend.php (__construct): Use object hash
as default identifier.
* VuFindSearch/Backend/Solr/Backend.php (__construct)
(setIdentifier): Inject backend identifier via setter, not
constructor.
* VuFind/Search/BackendManager.php (onResolve): Inject backend
identifier.
* VuFindSearch/Backend/BackendInterface.php (setIdentifier): Make
setIdentifier() part of the backend interface definition.
* VuFind/Search/Factory/SolrReservesBackendFactory.php (__construct):
  Dto.
* VuFind/Search/Factory/SolrDefaultBackendFactory.php (__construct):
  Dto.
* VuFind/Search/Factory/AbstractSolrBackendFactory.php
($serviceName): Removed. Name injected by BackendManager.
* VuFind/Search/BackendManager.php (onResolve): Inject backend
  identifier.

* VuFind/RecordDriver/AbstractBase.php (getSourceIdentifier)
(setSourceIdentifier): Implement RecordInterface.

* VuFind/Search/Solr/Results.php (performSearch): Pick records from
  RecordCollection.

* VuFindSearch/Backend/Solr/Response/Json/RecordCollectionFactory.php
(__construct, factory): Use factory function to create collection
records instead of classname.
* VuFind/Search/Factory/SolrDefaultBackendFactory.php
(createBackend): New function. Set RecordCollectionFactory with
factory function for SOLR records.

Created mailer factory to better separate VuFind-specific configuration issues from actual mailer functionality.

Started loading configurations through a custom plugin manager instead of static \VuFind\Config\Reader.

Fixed resolver drivers to use HTTP client instead of file_get_contents; this adds proxy support and improves testability.

Bugfix: Only convert month part from string to number if not already provided as number.
Error occures when input date has this format: 31/12/2013
Additional cleanup: Replaced deprecated split() with explode()