Changes in this PR:
- Upgrading WebJobs.Host.Storage to use v12 Azure storage SDK
  - New major version of WebJobs.Host.Storage
  - New public types for IDistributedLockManager implementation, IAzureBlobStorageProvider
- Removing Track1 Microsoft.Azure.WebJobs.Extensions.Storage from solution and build files (code remains in repo) 
- Migrating E2E and Functional Tests to use the Track2 Microsoft.Azure.WebJobs.Extensions.Storage packages