Bug 1036928 - Allow to set longer time estimages as 60 minutes

Closed the previous pull- working only on this branch now.
@bobsilverberg If I remove the code from two places in views.py, I would need to give the same in forms.py
Looking at the code, I fee I should add in the code in function def clean(self) in class TaskForm(forms.ModelForm)
Am I on the right track?