Create v2 branch with support to Py3 and CKAN >= 2.9 only

[aivuk]

Fixes #63

[codecov]

Codecov Report

Merging #66 (bd79867) into master (f151aa5) will increase coverage by 1.63%.
The diff coverage is 94.71%.

@@            Coverage Diff             @@
##           master      #66      +/-   ##
==========================================
+ Coverage   82.70%   84.33%   +1.63%     
==========================================
  Files          26       24       -2     
  Lines        2157     2088      -69     
==========================================
- Hits         1784     1761      -23     
+ Misses        373      327      -46     

Impacted Files	Coverage Δ
ckanext/validation/jobs.py	82.85% <83.92%> (-0.07%)	⬇️
ckanext/validation/helpers.py	88.88% <87.50%> (+9.40%)	⬆️
ckanext/validation/plugin/__init__.py	95.80% <90.90%> (-1.38%)	⬇️
ckanext/validation/logic.py	68.27% <94.59%> (-0.39%)	⬇️
ckanext/validation/model.py	100.00% <100.00%> (ø)
ckanext/validation/tests/fixtures.py	100.00% <100.00%> (ø)
ckanext/validation/tests/helpers.py	100.00% <100.00%> (+1.88%)	⬆️
ckanext/validation/tests/test_form.py	100.00% <100.00%> (+19.83%)	⬆️
ckanext/validation/tests/test_interfaces.py	98.11% <100.00%> (-0.06%)	⬇️
ckanext/validation/tests/test_jobs.py	100.00% <100.00%> (ø)
... and 10 more

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[ThrawnCA]

What's the benefit of ditching all the cross-version compatibility?