Use pycodestyle instead of PEP8

PEP8 was renamed to pycodestyle; this issue explains why:
https://github.com/PyCQA/pycodestyle/issues/466

This commit changes our tests to use pycodestyle instead of pep8.

It also means:
- making a couple of whitespace changes to appease the linter
- disabling warnings for bare `Except`s (ie `Except` instead of `Except
  ValueError`) – this seems like a sensible thing to catch but I’m not
  going to make meaningful code changes in this commit

app/models.py

@@ -153,6 +153,7 @@ class Service(db.Model, Versioned):
         default=BRANDING_GOVUK
     )
 
+
 MOBILE_TYPE = 'mobile'
 EMAIL_TYPE = 'email'
 
@@ -340,6 +341,7 @@ class TemplateHistory(db.Model):
                              nullable=False,
                              default=NORMAL)
 
+
 MMG_PROVIDER = "mmg"
 FIRETEXT_PROVIDER = "firetext"
 SES_PROVIDER = 'ses'