Fixing bug that was giving error when column or row coordinates would be in acceptable range.
Several new features

* New contructor what will receive a map of TFile* and a path and will pick up the plot pointed by that path from all TFile in the map.
* Implemented new scale method that takes as input a map of weights and will scale each plot that has a weight defined on that map
* Implemented new getMerged method that takes a vector of indexes will return a new histogram resulting from adding all plots on that vector
* Now included on cxx file explicit declaration of some classes implementing this template. This avoid linking problem.
Some typedefs to more ease of use of this classes implemeted by ICPlotCollection.