Add Support For Loading Image ByteArray During Preprocessing

[AlexandreBrown]

Currently we are forced to pass in a File when loading an image in the preprocess DSL.
It would be great to support the use case where we already have the images loaded and ready in memory instad of requiring to save them to the disk. This avoids a round trip to the disk and makes it more convenient to the user of the library.

[zaleslaw]

Thanks to the issue and proposed PR for this issue, we need to design in this place a better architecture to add new data sources more easily than now. It will be supported in the release 0.4

[AlexandreBrown]

@zaleslaw Hello, was this added in 0.4?

[zaleslaw]

@AlexandreBrown Unfortunately, it was not included

[juliabeliaeva]

Issue became obsolete since the new more flexible preprocessing dsl was implemented in #425. Dataset api also allows to accept different sources now with the DataLoader abstraction introduced in #424.