Refactor into an app factory [2 of 2] (#322)

* Replace all `from nyaa import app` imports with `app = flask.current_app` (or `from flask import current_app as app` where possible)
* Add a separate config object for top-level and class statements as `nyaa.extensions.config`
Required because those codes don't have app context at the time of evaluation/execution.
* Remove `routes.py` file and register all blueprints in `nyaa/__init__.py`
* Refactor `nyaa/__init__.py` into an app factory
* Update tools
* Update tests (temporary, will be replaced)

db_create.py

@@ -1,9 +1,11 @@
 #!/usr/bin/env python3
 import sqlalchemy
 
-from nyaa import app, models
+from nyaa import create_app, models
 from nyaa.extensions import db
 
+app = create_app('config')
+
 NYAA_CATEGORIES = [
     ('Anime', ['Anime Music Video', 'English-translated', 'Non-English-translated', 'Raw']),
     ('Audio', ['Lossless', 'Lossy']),