Warn user if Duration does not equal sum of actor task blocks

[darenwelsh]

Add a warning banner if the Duration does not equal the sum of (at least one of) the actor task blocks. For example, if a user states an EVA is 6:30 but they put a total of 7:00 of tasks on EV1, the timeline will extend beyond the margins of the timeline container (and it just doesn't make sense).

Related to #4.