Use QFreeList for timer id allocation

Use QFreeList for timer id allocation

The timer id allocator doesn't need a paylod (hence T=void), but we want
to tune the allocation 'strategy.' We allocate a maximum of 6 blocks
(like before), but the first block is twice as large as before and is
not static writable anymore. The initial value is 1 (0 is not a valid
timer id), but otherwise the constants are the same as the defaults.

Change-Id: Ied49ff4d7a6a8d69bc8c7bfa5475e4111446659f
Reviewed-on: http://codereview.qt.nokia.com/2161
Reviewed-by: Qt Sanity Bot <qt_sanity_bot@ovi.com>
Reviewed-by: Olivier Goffart <olivier.goffart@nokia.com>