Add required attribute in required fields

[franznoel]

2 page corrections are needed:

Event.html

In event.html, the following fields need required attribute:

• event type
• guest list

  Sign-in.html

In sign-in.html, all fields need a required field.

[franznoel]

Added required attribute in fields in event type and other fields in:

• event.html
• user-profile.html
• sign-up.html