Cleanup tox configuration

There were issues with dependencies and tox environments under Python 3
so refactored the tox configuration to be more consistent and clearer.

- Moved travis to default to Python 3 for linting and tests.
- Fixed missing mock for cairo in sphinx config.
- Collated the base deps sections to improve readability.
- Added PYTEST_ADDOPTS env to override pytest verbosity in just tox
  tests as this was a common option being used.
- Renamed env 'testcoverage' to the more concise 'coverage' and moved
  html creation under single env as handy to have this output as well
  as report.
- Cleaned up the isort config for gtk3.
- Added `bad-continuation` to pylint config as conflcts with black
  formatting.
- Fix isort issue with bbfreeze script. This will likely be removed
  in future so just skip sorting it.

1 files changed, 2 insertions, 1 deletions

diff --git a/packaging/win32/deluge-bbfreeze.py b/packaging/win32/deluge-bbfreeze.py
index 400bf640f..a58161882 100644
--- a/packaging/win32/deluge-bbfreeze.py
+++ b/packaging/win32/deluge-bbfreeze.py
@@ -10,7 +10,7 @@
 # the additional special exception to link portions of this program with the OpenSSL library.
 # See LICENSE for more details.
 #
-
+# isort:skip_file
 from __future__ import print_function
 
 import glob
@@ -19,6 +19,7 @@ import re
 import shutil
 import sys
 
+
 import bbfreeze
 import gtk
 from win32verstamp import stamp