identical filter are only once allowed in the filter-container

[l00mi]

if the users does try to add the same filter again, please fire an event (ideally with the id or a uniquie way to select the already existing data-filter)

[bergos]

This commit add the app.events.filterDuplicate event, which forwards all the filter parameters.

[l00mi]

implement a visual cue showing that the filter is already active. e.g. one of these:

• short glowing of the active filter
• shaking of the clicked button
• not allowing to click at all (different style and no pointer cursor)

[l00mi]

This issue was moved to zazuko/zack-search#12