Remaining task effort taking into account the time spent

We would find important to have an additional effort type, which take into account the time spent until today.

Before the start of the task we would define the overall task effort in hours (like the basic effort type).

Then, the workload chart will show for each task:

- for the past : the time spent (in replacement of the planned effort),

- for the future (today until the end of the task) : the remaining effort (in hours) = overall effort - time spent // the remaining effort (in hours/day) = (overall effort - time spent) / (end date - today())