Handle postgresql and sqlite3 libs properly

Do not fail to compile when one of them is missing but the other one is not.

Raise an error when trying to open a database with the missing library.

see #3237

src/database/database.cpp

@@ -15,8 +15,6 @@
 
 #include <memory>
 
-#include <sqlite3.h>
-
 std::unique_ptr<DatabaseEngine> Database::db;
 Database::MucLogLineTable Database::muc_log_lines("muclogline_");
 Database::GlobalOptionsTable Database::global_options("globaloptions_");