Add/remove exercise feature

[tarikhamilton]

Currently, you can only edit what has been created, which are three defaults. While you can rename them, it would be best if the user could track exactly what they consider important.

Requirements

As a user, I'd like to have as many exercise maxes as I desire.

• While in edit mode, add a green button under the latest row that says "Add".
• While in edit mode, add a third column and add a red button that says "Remove" on each row.
• Do not allow less than one exercise to remain.

Use the nanoid package for unique IDs.