Use flake8 if available instead of pyflakes

With flake8, we can check for more issues and ignore those who are not
real issues.

This allowed me to find genuine errors in:
- modules/boursorama/pages/account_history.py
- modules/ing/pages/login.py
- weboob/tools/application/qt/qt.py
I left one in weboob/tools/browser/browser.py for the time being.

Some PEP8 fixes on other files.

weboob/tools/browser/firefox_cookies.py

@@ -21,7 +21,7 @@
 try:
     import sqlite3 as sqlite
 except ImportError, e:
-    from pysqlite2 import dbapi2 as sqlite
+    from pysqlite2 import dbapi2 as sqlite  # NOQA
 
 from mechanize import CookieJar, Cookie
 
@@ -47,7 +47,8 @@ class FirefoxCookieJar(CookieJar):
 
     def load(self):
         db = self.__connect()
-        if not db: return
+        if not db:
+            return
 
         cookies = db.execute("""SELECT host, path, name, value, expiry, lastAccessed, isSecure
                                 FROM moz_cookies
@@ -83,12 +84,15 @@ class FirefoxCookieJar(CookieJar):
 
     def save(self):
         db = self.__connect()
-        if not db: return
+        if not db:
+            return
 
         db.execute("DELETE FROM moz_cookies WHERE host LIKE '%%%s%%'" % self.domain)
         for cookie in self:
-            if cookie.secure: secure = 1
-            else: secure = 0
+            if cookie.secure:
+                secure = 1
+            else:
+                secure = 0
             if cookie.expires is not None:
                 expires = cookie.expires
             else: