Add informations about slicer configuration in the JS Client API

Using the JS Client API to autolatically set up the slicers of many report depending on internal logic, we would like to have access to some settings directly in the API so that our code can adapt each slicer.

Here are the missing elements:

• the "kind" of slicer: is it a categorical slicer, a range slicer, a relative date slicer? The only way we have to "guess" it now is to use the "state" of the slicer and explore the filters inside the state. However when, the default values in the slicer are the full range of data, those filters does not exist, so we cannot guess it is a range filter or a relative time filter.
• the "single selection flag" : when we have a categorical slicer, if the report designer checked the "Single Selection" option, we have no way to get this settings in the client API and then we cannot know if we need to send only one value or many of them.

Regards