Add input validation on index.html to make sure user gives name to new *list*

[amjcurtis]

Current behavior: If user creates new list w/o giving it a title, currently the new list instance is saved w/ an empty string as its listTitle.

Suggested fix:
Option 1: If user doesn't give new list a name, assign a default name to the list (for example, "Untitled List"). Pros: This is the behavior you'd expect in most apps. Cons: We don't have any functionality for letting user rename an existing list so that they could change it from "Untitled List."

Option 2: If user doesn't give new list a name, alert them to add a name and don't let them move on to next page (lists.html) until they've done so. Pros: This would get around problem of not having any way for user to edit name of an existing list. Cons: None?

Ideas to include:

• 'required' attribute
• minLength, maxLength
• CSS styling like below:

input:invalid {
  box-shadow: 0 0 5px 1px red;
}

input:focus:invalid {
  outline: none;
}