Improve time-slider widget

[gannebamm]

Part of #27

Problem: As a creator, it is not possible for me to specify for the map widgets whether they should be filtered by time slider or not. As a result, some widgets, such as a pie chart, are misleading in their data display. An example of a map with corresponding widgets can be seen here. The feature is part of the following GitHub issues: GeoNode/geonode-mapstore-client#1473

Objective: As a creator, I would like to be able to configure for a widget whether a widget should accept the time-slider filter or not. This configuration is saved with the map. By default, the time slider is ignored.

[gannebamm]

see #41