Add BlobStoreManager.getRemainingLeaseQuotaBytes.

+ Add LimitExceededException which can be used to indicate
that an app is doing something that will cause it to violate
any limits enforced by the System.

Bug: 150239703
Test: atest --test-mapping apex/blobstore
Change-Id: I7584d1b8618be546080b0eddb2fe35de2611f9e7