Add 'clickFilterBehavior' to base-mixin to allow ctrl-click joins

The clickFilterBehavior option is intended for ordinal charts, bubble charts, pie charts, etc, i.e., those where clicking on an svg node filters to that node. I have not tested what would happen if a user trie do tenable on a brush filter for example. 

.clickFilterBehavior has 4 modes:
 - "replace": The clicked node replaces the current filter list. Note that it is not possible to remove the filter in this case without a reset link.
 - "toggle": Filtering for the clicked node is toggled from its current state. Therefore, if no filters are applied, clicking a node will filter all but that node (by applying an inverse filter under the hood).
- "replaceThenToggle": This is the current behavior. If there are no filters applied, act as 'replace'. If there is one ore more filter applied, act as 'toggle'. 
- "replaceCtrlToggle": This acts like selecting graphics objects in e.g. PowerPoint.  Left-click acts as 'replace', and ctrl-click acts as 'toggle'.