Rename package providers and remove GSON provider

Removed the GSON provider from the REST utils project. This
functionality will be duplicated in several projects as our technical
stack refuses to remove this duplicate code.

Renamed packge providers to jax_rs. Providers was too general, jax_rs
better describes what this code does.
Restructured Operator API and REST utils

Completely restructured both projects to have a more sane directory
structure.
Use REST utils in chargingstation-configuration

The chargingstation-configuration application now uses the REST utils
project instead of duplicating all of the REST code.