Add the ability to deny tags for flow filtering

[Wardenfar]

With theses changes, there are now required tags and denied tags.

Each flow must contains all required tags but none denied tags.

In the filter UI, the shift key acts as an effect inverter.

Click event rules table :

inactive => click => required
inactive => shift+click => denied

required => click => inactive
required => shift+click => denied

denied => click => inactive
denied => shift+click => required

In this example, GIF is required and SLOW is denied :

[aiooss-anssi]

Merged in #3, thanks!