LPS-37457 Splitting the LAR file

Hey Mike,

I've prepared the PR for the LAR splitting here it goes. A few remarks though on the code.

- Currently I am using the exported LAR's name to transfer the chunks over the network. This was just enough to make it work, when I'll work on the background task executor for remote staging this will be extended with the proper stuff of course
- I've added a new method in the FileUtil/FileImpl which will check the permission as well for the file writing following the existing patterns.
- I'm passing the httpPrincipal for the remote live as a service context attribute to the local service. I'm doing this because I wanted to highlight that this is not the remote service we are calling, this is a special parameter what will be used in the service implementation
- I've added a checksum checking method to make it sure that the file has been transferred correctly and we can kick-off the import and we are importing what we want to

That's all I think.

Thanks,

Máté