Manage Watchers dialog design review

Issues raised with the dialog design which need to be fixed:

• replace error icon with trash can a la JIRA
• add note about displaying users without access
• keyboard navigation: Escape to close, Tab to buttons (means removing links on user names.. boo )
• include Help link in button bar
• add vertical divider between sections if possible
• make heading text consistent with macro browser (different colour, slightly smaller).

(EACJ issue: https://extranet.atlassian.com/jira/browse/UI-1156)