Bee class API simplifications

[AuHau]

I have discovered few possible improvements:

Currently, there are "two ways" how to download a file, even though they are not related that much internally, but from external API point of view they seems similar. There is downloadFile and downloadFileFromCollection. I think these could be merged into downloadFile where its signature would be extended with optional parameter path to downloadFile(reference: Reference | string, path?: string) and if path would be specified than it would use "download file from collection" approach and if not specified than it would use "download file" approach. This would affect both downloadFile and downloadFileReadable.

Another suggestion is actually to drop the uploadFilesFromDirectory method and instead provide this functionality through utility function that would build collection and actually create new method uploadCollection as I have already proposed in #172 that you would pass the collection to.

Also another thing is that I would like to unify usage of the return type of Reference and ReferenceResponse choose one or the other and use it consistently. I would lean to use Reference I guess. Should verify that the responses does not contain some useful data in headers that should be extracted and passed along like with File object.

[AuHau]

The consensus is to move forward with the first and third improvements.

[AuHau]

Resolved in #280