[kwin] Add a test application for testing size increment

The test application can verify that KWin correctly interprets the
WM_NORMAL_HINTS as described in ICCCM section 4.1.2.3 for the
combination of min size, base size and size increment.

Introduces an optional dependency to xcb-icccm library. It's optional
as the last time we tried to use it build.kde.org didn't like it at
all. Thus it should be possible to disable building this test app if
the dependency is not found.