Connect streams with bokeh callbacks

holoviews/core/util.py

@@ -954,7 +954,7 @@ def get_dynamic_item(map_obj, dimensions, key):
     and a corresponding key. The dimensions must be a subset
     of the map_obj key dimensions.
     """
-    if key == () and not dimensions:
+    if key == () and not dimensions or not map_obj.kdims:
         return key, map_obj[()]
     elif isinstance(key, tuple):
         dims = {d.name: k for d, k in zip(dimensions, key)

holoviews/plotting/bokeh/__init__.py

@@ -17,7 +17,7 @@
 from ..plot import PlotSelector
 
 from .annotation import TextPlot, LineAnnotationPlot, SplinePlot
-from .callbacks import Callbacks # noqa (API import)
+from .callbacks import Callback # noqa (API import)
 from .element import OverlayPlot, BokehMPLWrapper
 from .chart import (PointPlot, CurvePlot, SpreadPlot, ErrorPlot, HistogramPlot,
                     SideHistogramPlot, BoxPlot, BarPlot, SpikesPlot,