Fixed T28222 Show histogram according to selected time point

+ Fixed T28221 with a quickfix (no dynamic label used in histogram)
+ Fixed T28223 with a quickfix (no dynamic label used in histogram)
+ Added a feature to QmitkSliceNavigationListener. One can now also

only listen to time or position changes and get the current
timepoint from the listner. This feature was added to avoid more
code dublication

+ Deactivated legend in Histogram widget as a quick fix optimzation.

As long as the name of the chart is hardcoded and only one image
is supported the legend is an unecessary wast of screen and reduces
the histogramm to much.