Support 31 mouse buttons (with platform plugins xcb and xlib).

Support 31 mouse buttons (with platform plugins xcb and xlib).

This commit includes changes for mouse button support within the XCB
and XLIB platform plugins. Support in other platform plugins will be
added in the future. The namespace update is prerequisite to compile
the the Plugins, and the update in qguiapplication.cpp is required for
the enhancements to actually work.

Task-number: QTBUG-22642
Change-Id: Ie18fca3b9c86d0b6abbf2103a4f8582e6ce83e7d
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
Reviewed-by: Samuel Rødal <samuel.rodal@nokia.com>