Search as you type should only start requesting when the minimum amount of charactars is reached

Since https://gitlab.com/gitlab-org/gitlab-ce/commit/da42dfb3cf4a2fb0cdcc1a3b41438516a0bed0e5 we only start searching when the search term is longer than 2 characters, before we return an empty collection.

In cases like the the group filtering we would display an empty list when the search term is too short.

I think we should only start sending requests when the term is long enough and make it clear to the user that they need to keep typing for search to start.