Rework ngeo.LayerHelper promise handling
Rework ngeo.LayerHelper promise handling

Do not use defer.
Reject failed promises.

ger-benjamin/ngeo,kalbermattenm/ngeo,pgiraud/ngeo,camptocamp/ngeo,pgiraud/ngeo,pgiraud/ngeo,camptocamp/ngeo,camptocamp/ngeo,ger-benjamin/ngeo,camptocamp/ngeo,kalbermattenm/ngeo,adube/ngeo,Jenselme/ngeo,adube/ngeo,adube/ngeo,ger-benjamin/ngeo,kalbermattenm/ngeo,Jenselme/ngeo,adube/ngeo,camptocamp/ngeo,Jenselme/ngeo,Jenselme/ngeo