Filters / #635

Some questions:

• views for projTasks involve:
  • settings for filter-list(s) none, one or more
  • which options are active in those filter lists
• mental note: could list_filter_options be derived from render_list?
  • feature:
    • single select / multiple select
    • update for second table
    • has focus
• what about filters that are no lists (like date and priority)