rename "django_ynh" -> "django2ynh"

[jedie]

see also #13

[codecov-io]

Codecov Report

Merging #15 (eebbc31) into testing (eb3fe62) will decrease coverage by 0.30%.
The diff coverage is 58.33%.

@@             Coverage Diff             @@
##           testing      #15      +/-   ##
===========================================
- Coverage    51.69%   51.39%   -0.31%     
===========================================
  Files           19       19              
  Lines          472      467       -5     
===========================================
- Hits           244      240       -4     
+ Misses         228      227       -1     

Impacted Files	Coverage Δ
django2ynh/__init__.py	0.00% <0.00%> (ø)
django2ynh/base_settings.py	100.00% <ø> (ø)
django2ynh/local_test.py	0.00% <0.00%> (ø)
django2ynh/management/commands/create_superuser.py	0.00% <ø> (ø)
django2ynh/path_utils.py	0.00% <ø> (ø)
django2ynh/pytest_helper.py	0.00% <0.00%> (ø)
django2ynh/secret_key.py	83.33% <ø> (ø)
django2ynh/sso_auth/user_profile.py	56.60% <ø> (ø)
django2ynh/test_utils.py	66.66% <ø> (ø)
django2ynh/views.py	47.05% <ø> (ø)
... and 12 more

---

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[jedie]

-> #13 (comment)