Refactored Query value object

This is a BC break. We have multiple ways of dealing with this:

1) Keep the $criterion property and use it for filters -- this would
   only be a minimal BC break

2) Keep the $criterion property and use it for the query -- this would
   not be a BC break, but leave us with very unclear semantics.

3) Break BC entirely (like implemented), which makes the query change
   obvious to the users.
Converted search service tests to just use filters for now
Adapted Legacy search implementation to use filter
Visit filter into Solr filter query
Updated test expectations: with filter queries we receive no scores any more
Introduced matchAll criterion
Added: Query parameter, where it makes sense
Fixed variable naming conflict
Implemented: MatchAll criterion visitor
Handle MatchAll criterion in legacy search
Removed $query parameter from findSingle() again

Since findSingle is used to locate exactly one item, the $query parametr
with applied scoring and fulltext matching does not make sense here.

Removing this parameter here, also means we will not break the API in
this regard.
Added: Additional properties to fulltext search criterion
Added: First unit test for Solr fulltext criterion visitor
Extracted field mapping into its own class
Implemented: Visiting of fuzzyness and boost on fulltext criterion
Tested: Boosting unknown field
Implemented: Integration tests for advanced full text search query
Merge branch 'master' into search-filter-refactoring
Use filter property instead of criterion property internally
Added: Default value before merging