Back-end: support new hobbies formation

[omrihuller]

follow up to #240

[Danielohayon]

Changed the UserSchema in the backend module to include a new array of hobbies that are blockers called blockers. Meaning that every hobby in the array hobbies is considered as a yes, every hobby in the blockers array is considered as a firm no, meaning a blocker. And finally every hoody that is not in the hobbies array and not in the blockers array is considered as a "Don't Care".

So the heuristic for calculating a match between two users will be as follows:

Person A/Person B	I am	Don't care	No way
I am	+1 to the matching sum	+0 to the matching sum	Matching result is set to 0
Don't care	+0 to the matching sum	+0 to the matching sum	+0 to the matching sum
No way	Matching result is set to 0	+0 to the matching sum	+1 to the matching sum