[IMP] add the posibility to merge the job. This is very usefull for the ...

...Magento case, indeed the api is very slow and we have to avoid the useless call to Magento, if we modify a binding and a product only one job should be created in order to avoid 2 call to Magento instead of one

You can take a look to this exemple : https://github.com/OCA/connector-magento/pull/23