Added resize parameters for dataset image reader, and the ability to loa...

...d data from alternate directories

cc @eickenberg 

Added the ability to specify arbitrary directories for the load_sample_images and load_sample_image functions to enable loading "other data" easily. 
basename is OK with me(I think this code came from sklearn originally). It would just be the name of the file from that directory - you can see the example usage in plot_multiple_localization.py. You would use it exactly the same just with an extra directory to allow for selection of a single file from an arbitrary location. Dealing with full paths that point to a file would be OK too but it gets hairier to figure out what the input represents (file name only vs. full path)