tags: REST API addition

Addition of  API and REST API for tags.
@greut , i am very sorry , i just saw this message. Maybe i could have the keys hard-coded or i could try to make the dictionary `to_update` and `OrderedDict`. In any case, this is just a test to see if the results match. Apart from that the code functionality is fine. Should i try to use `OrderedDict`, to ensure the order of the keys?