Reject rather than fail chapter in unwanted language
Add tests for download phase

test_batoto:TestBatoto. 88% coverage, mostly just excepts uncovered.
Add a test for irrelevant url handling

test_batoto:TestBatoto.test_irrelevant_url. 89% coverage.
Refactor invalid url tests

test_batoto:TestBatoto.(test_invalid_chapter, test_invalid_url and
test_irrelevant_url) merged into test_batoto:TestBatoto.test_invalid_urls
89% coverage.
Refactor chapter page tests

test_batoto:TestBatoto.(test_get_chapter_pages & test_chapter_language)
merged into test_batoto:TestBatoto.test_get_chapter_pages. 89% coverage.
Change invalid chapter entry url