Added 'reshape_on_bbox' method to the FramedImage class

[jnolan14]

Bruce wants the ability to reshape a volume to a target size, centered on the bounding box. Added the 'reshape_on_bbox' method to the FramedImage class. It calls self.bbox to get the bounding box, then adjusts that cropping to match the target size using 'fit_slicing_to_shape' and uses that to crop the original volume.

@ahoopes, not sure if it is better to have this be its own method, or if it would be better to put this in 'reshape' and reintroduce the 'center' argument.

[ahoopes]

cool this is a good idea

my preference is just adding an argument option like center='bbox' or something to reshape instead of introducing a new function because its a bit more minimal and the functionality is basically the same, but could go either way

[jnolan14]

Thanks, Andrew! I agree it would be a bit cleaner to fold the functionality into reshape, and would allow us to make the fit_to_shape hook fully backwards compatible. I'll add the functionality into reshape and update the fit_to_shape call