Days should have a minimum time spent

[AlexHalbesleben]

Days other than the current day should have a minimum time spent. The goal is to plan for future tasks that aren't known yet but probably will happen. Ideally, this is highly customizable--the option itself can be toggled, the minimum length can be adjusted, and the number of days in the future after which this takes effect can be adjusted.

The core issue is situations in which a set of tasks (e.g. college essays) are scheduled with firm deadlines but other tasks (normal homework, etc.) are not. When these new tasks are added, essays get pushed back because the algorithm thinks that future days will be less busy--even though this isn't necessarily the case.

This will necessitate a settings section once that is implemented (#118).