New class KOSRelease - a parser for os-release files

Summary:
Imported form KInfoCenter along with test case. This also includes a
license change from GPL to LGPL.

When working on Linux-centric software it may be necessary to get specific
information about the system beyond what may be obtained from QSysInfo.
This new class allows complete access to all information in the os-release
file as per the os-release "specification".

https://www.freedesktop.org/software/systemd/man/os-release.html

Test Plan:

• new test passes
• header installed
• camelheader installed
• kinfocenter can successfully find the header and link the new class in place of the old builtin one

Reviewers: apol, mpyne

Reviewed By: apol, mpyne

Subscribers: davidedmundson, pino, aacid, mpyne, kde-frameworks-devel

Tags: Frameworks

Differential Revision: https://phabricator.kde.org/D20092