Collaborator search glitches

[mpsonntag]

• When searching for a collaborator the time delay until the search is processed feels a bit too long.
• When a username has been entirely entered correctly, the suggestion list disappears. Leave the suggestion list to stress the point, that the username has been entered correctly.
• Test the search suggestions with different browsers. There might be a problem with displaying the suggestion list after a search string has been entered and shortened again in browsers other than chrome.
• Display suggestions only after entering at least three characters in the search string.

[mpsonntag]

Since it works quite similar, change the points above in the repo/user search as well.