Refactor frontend code

[Benjozork]

Motivation

• Many services have different APIs and sometimes behaviour; this can lead to bugs and headaches when implementing functionality
• Many backend paradigms are hard to express in the current frontend code

Solution / Tasks

• Make Resource a thing on frontend (excluding our reflection extensions like slice(), instantiate(), etc.)
• Genericize frontend services
• Rework auth code

[ranile]

Auth code has been reworked some time ago with the merge of frontend-rework branch