Update labels in gitlab-ui to use interactive popover

gitlab-ce~9594407 since GitLabbers use labels heavily.

Problem to solve

We currently have links included in label tooltips, which are not particularly helpful as tooltips disappear as soon as you hover outside the element.

Screen_Shot_2019-03-14_at_6.59.15_AM

Design Solution

Labels New label form
links_in_labels Label_Popover
| New label form | Labels | | ------ | ------ | | Screen_Shot_2019-10-30_at_12.48.57_PM | Screen_Shot_2019-10-30_at_12.49.08_PM | | Links should be blue, scoped labels `?` should link to docs | Convert description `input` to `textarea`; add markdown help text | Previous design From @cperessini's comment in gitlab-design#282 (comment 150466105)

Screen_Shot_2019-03-14_at_6.58.24_AM

Blocked by: !855 (merged)

Edited by Holly Reynolds