Fix 0011554: Status legend should react to current filter settings

The status legend shown at the bottom of the view all issues page should
factor in the current filter settings.

The following conditions should apply to showing the status legend:

• Don't show the legend if there is only one status selected by the
  filter
• Hide statuses from the legend that are hidden by the 'hide status'
  filter (for simple filters)
• Hide statuses from the legend that aren't selected using an advanced
  status filter