GitLab

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

Instead of a deprecated one, use upstream's cmake variable.

Stick it to the last tag for now, master isn't building.