Use resourceId from eventSource if it exists

[julienboulay]

This pull request allow to add resourceId defined on an eventSource and propagate it to the eventDef.
Fixes issue https://github.com/fullcalendar/fullcalendar-scheduler/issues/124

[acerix]

Thanks for the PR

[arshaw]

thanks for this @julienboulay . i want to merge this. could you please first sign this? https://docs.google.com/forms/d/e/1FAIpQLScU-HzFWsMRe1YcC_flGjIFRV_xm8nzRz1bIzUzSOMoA3AevQ/viewform?c=0&w=1

[julienboulay]

@arshaw : I've signed the agreement. Just one remark before merging. It seems that this code is obsolete and I could manage the resourceId with eventDataTransform.
Not sure that this pullrequest is necessary actually

[arshaw]

thanks @julienboulay . i think this feature is still valuable. it's more elegant that using eventDataTransform

[arshaw]

if you get a chance, could you write an automated test? https://github.com/fullcalendar/old-docs/blob/wiki/Automated-Tests.md