Python API instead of YAML (#1)

Added locales and made code easily and efficiently usable from Django

Can now be used from Python thanks to data structures instead of YAML.
Which means it can be used from django as well.

Replaced pybars3 by Django's template engine.

Made text a bit smaller.

No longer calculating totals, since they are already calculated from user's code.

Business's information and PDF page counter are now in the template file to allow easy edits.

• Moved templates folder + localizing dates + style edits

• ./documents/invoice/template -> ./template
• Dates are no localized using Babel.
• Removed wrapping in the table headers
• Centered table headers and short data cells
• Added localization

• Translated to French and German.

• Additional information can be added through the Executive model

• Additional information are now in the bottom center

• logo is now SVG
• added shipping total
• gross total is now bold
• date to pay until can now be omitted

• Must now specify the product's reference + discounts

• Now showing product reference instead of the product position
• Now showing the sum of discounts
• Added a filter: base65, will be useful in the future in an external way.