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)

tests/__init__.py

@@ -3,7 +3,7 @@
 import os
 import unittest
 
-from nyaa import app
+from nyaa import create_app
 
 USE_MYSQL = True
 
@@ -12,6 +12,7 @@ class NyaaTestCase(unittest.TestCase):
 
     @classmethod
     def setUpClass(cls):
+        app = create_app('config')
         app.config['TESTING'] = True
         cls.app_context = app.app_context()