breack the many2many relationship

add a contact_group_link model with 2 belongsTo
Contact hasMany contact_group_links
Group hasMany contact_group_links
commit contact_group_link while updating a Contact
use Group as View.select.optionvaluePath when updating a Contact
delete old contact_group_links while uptading a Contact
[Fix] error 'while inFlight' @ Contact update
try to manage contact_group_links @ Contact creation
try deffered contact_group_link creation @ Contact creation
deferred contact_group_link creation @ Contact creation
manage contact_group_links @ Contact deletion
Merge pull request #13 from Kcnarf/relationship-persistancy(2)

Relationship persistancy(2)