Python 3.7 and package updates

Merge pull request #13 from moltob/feature/cl

preparing 4.4.6

Salutation fix

v4.4.5

upgrading travis' default packages

Django 2.0.3

Merge pull request #11 from moltob/feature/django-2.0.3

Feature/django 2.0.3

Django 2.0.1

v4.4.3

changes

Customer notes in invoice screens

Merge pull request #10 from moltob/feature/customer-notification

customer notes during invoice creation

Currency & PDF default template

v4.4.1

changed default print style to letterhead

PDF template with letterhead

v4.4.0

updated

Fix sales report

Merge pull request #6 from moltob/hotfix/4.3.1

sales fix

Sales reports

• Added sales reports:
  • Overall
  • Yearly income
  • Tops & flops articles
• Updated to Python 3.6.2.
• Updated to latest versions of dependencies.

Beautification

• icons
• welcome screen