Annotate Exception/Solr, superseded by VuFindSearch exceptions

* VuFind/Exception/Solr.php: Add annotation as reminder to remove this
  class.
Add MultiIndexListener
Remove Worldcat/Backend::similar()

* VuFindSearch/Backend/WorldCat/Backend.php (similar):
  Removed. Not longer required by BackendInterface.
Move similar() to MoreLikeThis feature interface

* VuFindSearch/Backend/BackendInterface.php (similar):
  Removed. Defined by MoreLikeThis feature interface.
* VuFindSearch/Backend/Solr/Backend.php: Implement feature
  interface.
* VuFindSearch/Feature/MoreLikeThis.php: New file. MoreLikeThis
  feature.
Added WorldCat QueryBuilder test.
Merge branch 'search-refactor' of ssh://vufind.git.sourceforge.net/gitroot/vufind/vufind into search-refactor
Move handler name normalization from generic Query to Solr QueryBuilder.
Some backends have case-sensitive handler names!
Created separate class for building Summon queries.
Unit test included; wired up in place of old buildQuery() method.
Correctly configure query builder in Solr Backend Factory.
Progress on Summon search backend -- now using it for single record retrieval.
Fixed comment.
Initial integration of new search backend for Summon searching.
Still to do: reduce reliance on raw response.
Moved spelling into Summon RecordCollection.
Moved database recommendation retrieval into RecordCollection class.