Fixed filter removal bug

[Mogball]

To fix issue #3429 and a few other UI bugs with the slice filter.

• Having multiple filters then removing a filter by clicking "-" would clear the filter selections for those below on the UI
• Due to filter selection choices stored in Filter components as state, which are not updated when removing a filter
• Changing filter operator from type of array to string or vice versa does not properly transform the currently selected values
• Changing the filter column keeps the previously selected choices

Solutions

• Filter choices are stored as an array in the FilterControl component state and modified as filters are added, removed, or changed
• These choices are passed down to Filter components as props
• When changing the filter column, the selection values are cleared as per their type (array or string)
• Changing filter operator properly converts between array and string as needed

[coveralls]

Coverage remained the same at 69.119% when pulling 06eebae on Mogball:mogball/bugfix/slice_filters into 8223729 on apache:master.

[coveralls]

Coverage remained the same at 69.119% when pulling 5de6325 on Mogball:mogball/bugfix/slice_filters into 8223729 on apache:master.

[mistercrunch]

The tests for FilterControl are pretty skinny at the moment, would you mind beefing them up a tad?
https://github.com/apache/incubator-superset/blob/master/superset/assets/spec/javascripts/explore/components/FilterControl_spec.jsx

[coveralls]

Coverage decreased (-0.007%) to 69.112% when pulling d798f47 on Mogball:mogball/bugfix/slice_filters into 8223729 on apache:master.

[coveralls]

Coverage decreased (-0.007%) to 69.112% when pulling d798f47 on Mogball:mogball/bugfix/slice_filters into 8223729 on apache:master.

[coveralls]

Coverage decreased (-0.007%) to 69.112% when pulling d798f47 on Mogball:mogball/bugfix/slice_filters into 8223729 on apache:master.

[coveralls]

Coverage decreased (-0.007%) to 69.112% when pulling d798f47 on Mogball:mogball/bugfix/slice_filters into 8223729 on apache:master.

[coveralls]

Coverage increased (+0.02%) to 69.14% when pulling 719c823 on Mogball:mogball/bugfix/slice_filters into 8223729 on apache:master.

[coveralls]

Coverage increased (+0.02%) to 69.14% when pulling 719c823 on Mogball:mogball/bugfix/slice_filters into 8223729 on apache:master.

[coveralls]

Coverage increased (+0.02%) to 69.14% when pulling 719c823 on Mogball:mogball/bugfix/slice_filters into 8223729 on apache:master.

[Mogball]

Added some unit tests and increased code coverage a tad bit @mistercrunch

[mistercrunch]