Introduce QXcbXSettings

This allows you to easily retrieve properties in the XSETTINGS
specification. It is also possible to add listeners to get notified when
a specific property changes.

XSETTINGS is lazy initialized, so it will not be instansiated before
someone uses it. For now the intended use is a fallback for finding
cursor theme

Change-Id: Id47f0613f5876424cd47d721b40da17d3f63429e
Reviewed-by: Samuel Rødal <samuel.rodal@digia.com>
Add QXcbConnectionGrabber class

Inspired by QMutexLocker

Change-Id: I66e31091d2a006db3272b627567d95d3e0b1c4f9
Reviewed-by: Samuel Rødal <samuel.rodal@digia.com>
xcb: fallback to gtk cursor themes

When Xcursor LoadCursor fails to find a cursor

Task-number: QTBUG-27537

Change-Id: I46086c78c3d5bea3c39187dcc55b4774e58f5749
Reviewed-by: Samuel Rødal <samuel.rodal@digia.com>
Add BypassWinowManagerHint

Change-Id: Iaf04172aa4fce8d6b354c1c1fc3c376831ee8e91
Reviewed-by: Andy Nichols <andy.nichols@digia.com>