add and remove functionality for enzo todos

[1ntEgr8]

As of now, the only way to add or remove a todo is to edit $HOME/.enzo.config.yaml. This can be intimidating, and is error-prone.

Implement add and remove functionality from within enzo todo so that adding and removing tasks is super simple.

[1ntEgr8]

initial thoughts on implementing this:

• the user will enter their response in a popup
• cursor moves to the input location
• turn off raw mode, display the cursor
• read from stdin
• add a new todo to app state
• turn on raw mode, hide cursor, remove popup