Allow Schema upgrade of data model without breaking data refresh

[fbcideas_migusr]

Scenario. Import a data model into Power BI (say via excel file stored on onedrive). Setup a data refresh on it. Validate that it works. Now make a schema change in the data model (say add a new table). Save the file in the onedrive location. This now breaks the data refresh from the power Bi site. It would be quite common for users to keep updating the model schema as they go. Doing that should not impact the scheduled refresh functionality.