Third party S3 services support + #61

[stefanofornari]

This pull request should finalize the work to seamlessly support 3rd party S3 services like minio. It brings three main improvements, which I kept together as they are small enough and they complement each other.

1. All information to build a file system (bucket, endpoint, credentials, etc.) are now encapsulated in a S3NioConfiguration object that is passed to the constructor; this simplifies quite a bit the constructors and the need of accessors. This should also close File System settings #61

2. Deprecation of constructors taking a URI: in the NIO world, the FileSystem object is usually create indirectly, by the provider or even more subtly by using Files or Path; it is therefore cleaner the provider digests the URIs creating a corresponding configuration object that can then be passed to S3FileSystem's constructor. This brings also the valuable advantage of making the file S3FileSystem completely independent by the URI used to create and configure it.

3. Last but most importantly, it introduces a new file system provider, which manages the s3x:// URI schema as per the following URI pattern (as discussed earlier in other tickets and PRs):

   s3x://[key:secret#@]hostename[:port]/bucket/key

Thanks to bullet 1 above, it handed up to be quite clean, as the new S3XFileSystemProvider extends S3FileSystemProvider with very little code, while S3FileSystem is i completely in common between the two providers.

@markjschreiber , let me know what you think

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[markjschreiber]

Looks great. There is one minor comment about some if statements that appear to not be indented but I think we are looking good.

[stefanofornari]

fixed, thanks!

[markjschreiber]

Thanks for this contribution and for adding support for alternative S3 providers. I will bump the minor version later this week and make a release to maven central.

[stefanofornari]

@markjschreiber do we have the new version on central?
Also, I have created a couple of minor "cleanup" PRs. Would you mind review and merge them as well?