Updated the EventHubsCaptureEventGridDemo sample

[spelluru]

Updated the sample used by the tutorial:
https://review.docs.microsoft.com/en-us/azure/event-hubs/store-captured-data-data-warehouse?branch=pr-en-us-197006

1. Upgraded the Azure function project FunctionEGDWDumper. Now, the first parameter for the function is of type EventGridEvent and the second parameter is of type ILogger.
2. Updated the code after updating the two parameters.
3. Now, the code uses StorageSharedKeyCredentials that's built using the storage account name and the storage access key. Earlier, I had to set the access level for the container to "public" to get the tutorial working.
4. Updated the template JSON file to set the new configuration values for storage account name and storage account key.
5. Removed unnecessary DWDumper from the folder and the solution.
6. Cleaned up Readme.md file to point to the tutorial article on DOCS. This would eliminate duplication of the content. Also, removed all the images used by the old Readme file.