QmlProfiler: Add model template for range data

In order to unify the uses of range data and the calculation of first
and last ranges in visible areas we need a template class to provide the
respective algorithms.

Change-Id: I1c2e9c9fa9ae048262026236c4ff39017ab7913f
Reviewed-by: Kai Koehne <kai.koehne@digia.com>