Problem

• Uses can add more than 2 usernames into the Timeline's input box, either via URL parameter or by using the arrow keys on the keyboard to open the suggestions.

Example

https://tools.wmflabs.org/interaction-timeline/?wiki=metawiki&user=TBolliger%20(WMF)&user=Cats&user=Cats%20%26%20Dogs%20Guy&user=Cats%20%26%20dogs%20forever&user=Forr3st&user=1%20(New%20York%20City%20Subway%20service)&user=2%20%2B%202%20%3D%205&user=3%202%201%20booom&user=4%200%204&user=SPoore%20(WMF)&startDate=1512331200&endDate=1512417600

Acceptance criteria

• If a user forces an additional user via URL parameter it's their fault — that's just user error. Ideally it shouldn't break the timeline.
• Only the first two usernames should be supported.
• The username inputbox should not provide suggestions if two usernames are already entered.