Reposition multiple issue board title/selector dropdown

Resources

PM @victorwu | UX @dimitrieh

Part of

https://gitlab.com/gitlab-org/gitlab-ce/issues/25698 Issue board as a workflow tool

Problem

The positioning of the multiple issueboard dropdown is less then ideal imo and currently takes up a lot of vertical space:

Solution and design

This will be a temp solution and should be a quick fix to solve the vertical space and aesthetics of the issue board

Notes

This was a proposal that was considered here: https://gitlab.com/gitlab-org/gitlab-ee/issues/929#note_16184188 image

I however think this should be placed elsewhere: image

We can then if we want add the possibility for starred/extra important issue boards like so: image

This being flexible with the design, perhaps to flexible.. what are your opinions on this @hazelyang @awhildy