Test for add new filter state

[gogonzo]

I mean shiny tests covering insertUI, removeUI in FilteredData to cover uncharted territories. These are

• add new filter state
• check add_filter_state ui (added column should be excluded from the choice lists)
• check if the card exists
• check if the dataset summary changed
• remove single filter
• remove datasret filters
• remove all filters
• check if the var can re-added and removed again

[gogonzo]

These are well covered in the tests