smaller fixes and "security" measures

- move the OAuthSession class into util.py
- block special extractors for reddit and recursive
- ignore 'only matching' tests for testresults script

scripts/build_testresult_db.py

@@ -9,7 +9,7 @@ sys.path.insert(0, os.path.realpath(ROOTDIR))
 from gallery_dl import extractor, job, config
 
 tests = [
-   ([url[0] for url in extr.test], extr)
+   ([url[0] for url in extr.test if url[1]], extr)
    for extr in extractor.extractors()
    if hasattr(extr, "test")
 ]