DbLib: Add single-row query cache

Since single-row queries are performed rapid-fire during certain actions like
stepping through the symbol browser, there is high value in caching them for
a small amount of time.  The default cache parameters will keep results for
10 seconds, which errs on the side of getting fresh data from the database
on most user interactions.

eeschema/sch_plugins/database/sch_database_plugin.cpp

@@ -236,6 +236,8 @@ void SCH_DATABASE_PLUGIN::ensureConnection()
 
             THROW_IO_ERROR( msg );
         }
+
+        m_conn->SetCacheParams( m_settings->m_Cache.max_size, m_settings->m_Cache.max_age );
     }
 }