Apply Authorization headers in Job instead of in each Job implementation.

Summary:
Currently each Job adds the Authorization header, this patch centralizes this operation in Job.

See [[ https://phabricator.kde.org/D19948 | D19948 DRAFT Add Standard Query Parameters support ]] for previous discussions.

Reviewers: dvratil

Reviewed By: dvratil

Subscribers: kde-pim, #libkgapi

Tags: #kde_pim, #libkgapi

Differential Revision: https://phabricator.kde.org/D20883