Feature: #465 - Updated backend views

See Issue #465

Description

The view of the backend module were refactored. This has the following benefits:

• No inline CSS which avoid problems with Content-Security-Policies.

• Clearer design.

• Responsive design (old design was not usable on smartphones).

• Order tables with colors to improve the visibility of status of orders.

• Backend CSS reduced / updated to really used HTML.

Impact

Own overwrites might need adaption otherwise this change should not have any negative impact.