=== Problem to solve
The tool does not provide the users visual feedback if the tool has broken, is loading, or if the user has done something incorrect.
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=== Acceptance criteria
[] In the same place as the loading indicator (T180083) display the following messages:
[] If only one username has been provided, or if the wiki has not been provided — "Please provide two usernames and wiki to begin."
[] This can be displayed on the timeline by default as a zero state.
[] ~~If there are no edits to show but the users have interacted in the past — "(alert icon) There are no edits to show during the selected date range."~~
[] ~~If the users have never interacted in the past — "(alert icon) These two users have never interacted on the selected wiki."~~
[] If there are no results, display "(alert icon) No Results"
[] Use a Bootstrap alert dialog to display these errors:
[] General timeout/failure — "(alert icon) Something went wrong. Please reload or try your query again."
[] Invalid date range (e.g. start date is 2017 while end date is 2016) — "(alert icon) Invalid date range."
[] Do not allow users to type in the Users input box if there are already two names
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=== Notes
* The inputs already prevent selecting invalid usernames and wiki.