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.
Disable nonfunctional from_group test
Add a test for multiple chapters with same id

test_batoto:TestBatotoRewriter.test_chapter_id_match_multiple.
89% coverage.
Change series used to test parserless matching

Series receiving a new upload breaks this test, so swapping to a
series less likely to be updated.
Caching of series pages

Series pages will now only be fetched once per run and will last for
an hour.
Also fixes bug in url_rewrite where different chapters could be
identified as the same and rejected by seen.
Add support for --no-cache
Quieten debug messages
Ensure any rewritten entries are learned by seen

Also adds an optimisation to prevent getting the first page of
chapters twice.
Tweak error messages
Prevent url rewriting if plugin not loaded for task
Change to downloading pages internally

Uses methods from download.py. Allows the chapter to stay as one
lump rather than splitting into a large number of entries.
Change to downloading pages internally

Uses methods from download.py. Allows the chapter to stay as one
lump rather than splitting into a large number of entries.