Issue Vue app tech debt

• Duplication between some components. Most notable & confusing is the form. https://gitlab.com/gitlab-org/gitlab-ce/blob/master/app/assets/javascripts/notes/components/issue_comment_form.vue & https://gitlab.com/gitlab-org/gitlab-ce/blob/master/app/assets/javascripts/notes/components/issue_note_form.vue I would think we should have 1 form component for it & then just disable/remove the things the form doesn't support.