changed date format to 'yyyy-mm-dd' in invoice and transition raports
deleted useless file
moved generate_localized_pdf(..) to inkpy
code cleanups (import order, flake8, etc.)
better lang for docs generating
Merge branch 'develop' into report-date
call generate_pdf with lang_code arg
fixed imports order
removed using formats/
added a note about GENERATED_DOCS_LOCALE in docs
changed default value GENERATED_DOCS_LOCALE to None
Merge pull request #292 from xliiv/report-date

iso-date in pdf reports