RFC: Dockerfile based on Qt 5.12 and clang

Authored by apol on Jan 11 2019, 1:08 AM.

Description

RFC: Dockerfile based on Qt 5.12 and clang

Summary:
Instead of bringing the Qt binaries it builds our own.
It also finally solves some annoyances like including openssl by default.

Test Plan: I plan to test it, haven't tested yet.

Differential Revision: https://phabricator.kde.org/D18173