Addon code alignments

[FinalAngel]

• Extended test matrix
• Added tox and adapted imports
• Adapted code base to align with other supported addons

General

• [x] Update changelog Adapted code base to align with other supported addons
• [x] Add contributors text to README file We're grateful to all contributors who have helped create and maintain this package. Contributors are listed at [link to https://github.com/divio/djangocms-video/graphs/contributors].
• [x] Check that python, django, django-cms and other versions are listed correctly (add badge)
• [x] Make sure Django is not pinned in setup.py
• [x] Align gitignore files
• [x] Align setup.py
• [x] Keep the two line rule

Tests

• [x] Make sure naming for the test files is test_.py
• [x] Add tests_migration.py file if missing
• [x] Remove test migration check in other files
• [x] Check requirements.txt file for accuracy (e.g. unpin djangocms-helper)
• [x] Check settings.py that it is ordered correctly
• [x] Added isort and updated files

Internal

• [x] Run internal checklist

[codecov-io]

Codecov Report

Merging #8 into master will increase coverage by 1.13%. The diff coverage is 86.95%.

@@            Coverage Diff             @@
##           master       #8      +/-   ##
==========================================
+ Coverage   35.89%   37.02%   +1.13%     
==========================================
  Files          10       11       +1     
  Lines         390      397       +7     
  Branches       44       44              
==========================================
+ Hits          140      147       +7     
  Misses        249      249              
  Partials        1        1

Impacted Files	Coverage Δ
djangocms_modules/cms_toolbars.py	0% <ø> (ø)	:arrow_up:
...les/management/commands/update_modules_language.py	0% <ø> (ø)	:arrow_up:
djangocms_modules/apps.py	100% <100%> (ø)	:arrow_up:
djangocms_modules/migrations/0001_initial.py	100% <100%> (ø)	:arrow_up:
djangocms_modules/models.py	54.79% <100%> (ø)	:arrow_up:
...ocms_modules/migrations/0002_auto_20190122_0412.py	100% <100%> (ø)
djangocms_modules/handlers.py	17.5% <100%> (ø)	:arrow_up:
djangocms_modules/forms.py	41.07% <50%> (+1.07%)	:arrow_up:
djangocms_modules/cms_plugins.py	29.57% <85.71%> (+0.49%)	:arrow_up:

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