Add .gitignore
Refactored SOLR sendRequest

* VuFindSearch/Backend/Solr/Connector.php (createClient): New
  method. Create HTTP client for (url, method).
  (send): New method. Send request and return response.
  (query): New method. Prepare a SOLR query.
  (sendRequest): Removed. Refactored to send(), query(),
  createClient().
  (resubmit, getTerms, alphabeticBrowse, select): Use new method
  query().
Adjust Backendtest for modified Backend constructor
Rename lastRequest to lastQuery

* VuFindSearch/Backend/Solr/Connector.php ($lastQuery): Renamed
  from $lastRequest.
  (getLastQueryParameters): Dto.
  (resubmit): Dto.
  (query): Dto.
* VuFindSearch/Backend/Solr/Backend.php (search): Dto.
Apply defaults, appends, and invariants to resubmitted request

* VuFindSearch/Backend/Solr/Connector.php (resubmit): Apply defaults,
  appends, and invariants to resubmitted request.
Auto-detect method, remove optional method argument

* VuFindSearch/Backend/Solr/Connector.php (query): Auto-detect
  method, remove optional method argument.