Organized ClusterMergeAlgo + a bit of speed improvement.

    (*) Decoupled I/O and algirthm execution part
    	- Still works as an analysis unit
	- Now also work as an algorithm
    (*) Use cluster_merge_info, dedicated struct for merging => this makes it cleaner to move into LArSoft
    (*) Added book-keeping vector for merged cluster sets
    	- isInCluster() does not need to loop over to search for index
    (*) Added handles to set cut/detector parameters

Kazu
MINOR:

	(*) Comment added
	(*) Undo singleton design for ClusterMergeAlgo

Kazu