Rename addBlob!(..., filepath::AbstractString, ... ) to uploadFile and implement addBlob! that matches the api

[Affie]

          We should rather call this `uploadFile` and have an `addBlob!` that matches the api. 

I haven't had a use case for uploadFile yet, but it's good to have as I can see some uses.

Originally posted by @Affie in #264 (comment)

[dehann]

Old addBlob! Is still there unchanged. This is a different signature. Signature parameter tells user it's a file. End result is still that a blob was added.

[Affie]

To work seamlessly across the different back-ends signatures such as addBlob! should look the same, ie. addBlob!(store::AbstractBlobStore, blobId::UUID, blob)