Search filter bar for issues dashboard list

• Update the UI on https://gitlab.com/dashboard/issues with the search filter bar.
• My reaction is not included in this iteration.
• The filter options should be consistent with the designs in &454.
• This iteration will not have weights in Starter+, since the current implementation doesn't have weights. We have a separate iteration (https://gitlab.com/gitlab-org/gitlab-ee/issues/7928) to add the weight filter.
• When you load the page, the assignee filter is pre-selected to yourself, as shown in the screenshot below. (This is consistent with the current design due to performance issues of loading everything if no filter is selected.
• If you attempt to have no filters entered, you will get a message, again consistent with the current implementation.