Refactor code to use new timepoints dataset for existing app functions

[bhavyaac]

UPDATE 07/29/2021: Now that the dataset including the new timepoints is available, I should refactor the code so that the app functions as usual using only the this file (since it includes all of the joint_mouse, joint_pons, and joint_cortex data used in the current app). Once the app is functioning as usual using this file, I can move on to visualizing the new timepoints data.

The joint_mouse datasets (likely) include all of the information contained in joint_pons and joint_cortex datasets, but joint_mouse, joint_pons, and joint_cortex are all used within the app. Aim to change the code to use joint_mouse datasets only, to decrease the number of referenced datasets and therefore require less storage space.