Extended functionality to be able to fill 2D and 1D weighted histograms wiht string labels

The fillers (1D and 2D) were restructured to allow histograms filling with string labels in additional cases. For 1D histograms - support now the filling with string and arbitrary weight For 2D histograms - support all the combinations: string-double, double-string, string-string and double-double, all of them with an arbitrary weight.

In addition: added option for timer to report other units. Tagging @damazio Cleaned filling code in general, tagging @cburton @ponyisi @fwinkl - maybe this can be streamlined further Additional protection was added for Monitored::Collection so that it does not accept a temporary containers. Else the collection is deleted before the actual filling and values from it are needed. We only had this in UT.