Add ability to move up/down in list

[josegonzalez]

Sometimes you don't really care to reorder the entire list but just one or two entities, and having a helper method for this would be useful.

[ADmad]

For single entity you can just save it with position you want and the position of other records in the list will be adjusted as required. I guess methods moveUp(), moveDown() could be added to save writing 2-3 lines of code.