Once a task end date is changed forward, its dependents are also updated.
This fix makes sure that if some of those dependents are children of a
dynamic task it too is updated.
This may add a lot of overhead because dynamic tasks with many children
will be updated once for every one.
Fix to allow removing dependencies from a dynamic task.
Fixes on the PDF generation of Gantt charts. Still not perfert but much
better:

- Doubled the maximum number of lines.
- Pages are now properly created in the PDF
- If using multiple pages, all use the same time range.
Gantt charts now show the actual unit of the durations instead of
converting everything to hours.
Fix so that deleting a task log with a completion of 100% will lead to
a recalculation of the actual percentage, instead of simply assuming
that the method is called only on insertion and screwing up.
Fix to make sure a parent dynamic task has its completion state updated
when a child gets or loses a task log changing that task's completion
state.