Add basic pology posieve request support

Summary:
Configuration dialog
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I've added an option to posieve.py previously to allow a launch on a single entry. This is just a start, the goal is to have a better integration of Lokalize as a retriever of pology information and not only as a client for pology.

Reviewers: #localization, aacid, ltoscano, mlaurent

Subscribers: #localization

Differential Revision: https://phabricator.kde.org/D15181