Add setting for default search backend. (#1476)

config/vufind/config.ini

@@ -97,6 +97,9 @@ defaultModule   = Search
 defaultLoggedInModule = MyResearch
 ; When defaultLoggedInModule is used, this action will be triggered (default = Home)
 ;defaultLoggedInAction = Home
+; The search backend that VuFind will use in search boxes when nothing else is
+; specified (e.g. on user account pages, search history, etc.). Default = Solr
+;defaultSearchBackend = Solr
 ; The route VuFind will send users to following a log out operation. Set to false
 ; or omit to attempt to retain the user's current context after log out.
 ;logOutRoute = home

themes/bootstrap3/templates/search/searchbox.phtml

 <?php
     // Set default value if necessary:
     if (!isset($this->searchClassId)) {
-        $this->searchClassId = 'Solr';
+        $config = $this->config()->get('config');
+        $this->searchClassId = $config->Site->defaultSearchBackend ?? 'Solr';
     }
 
     // Load search actions and settings (if any):