"If Need Be" Scheduling Option Request

[gcassel]

Is your feature request related to a problem? Please describe. I love the general UI of crabfit, but it apparently does not enable users to indicate non-preferred time slots with "if need be" (or an equivalent). Some other scheduling apps have this option, and some of my groups use it regularly.

Describe the solution you'd like I'd like users to be able to toggle their inputs for time slots and ranges through yes, if need be and no options. This could be technically implemented for single time slots by enabling users to repeatedly left-click those slots to toggle their input through all three options. It seems trickier to combine that feature with the current ability to "drag and select" a sequence of time slots together, but there are at least a couple of potential workarounds:

1. Enabling a repeat of the same drag and select operation to toggle from yes to if need be to no. (This could be tricky however for a person with an imprecise mouse or motor skills.)
2. Enabling a right-click on a previously selected sequence of time slots to toggle that sequence's status.

[altsalt]

Related to #131

[GRA0007]

Thanks for the request @gcassel, and for the suggestions of how you think the UI should function. I'm going to mark this as a duplicate of #131.