Added the Copy / Move to functionality on the ISite interface

[MathijsVerbeeck]

Added the possiblity on the Site object to migrate files / folders in the current site collection or between different site collections. Also added the possibility to check the progress and a function that will wait until all the jobs have finished

Added functions:

• CreateCopyJobs(Async)
• GetCopyJobProgress(Async)
• EnsureCopyJobHasFinished(Async)

Issue ref: #414

[jansenbe]

Wow, that was fast @MathijsVerbeeck! Thanks again for the great work, this is another great addition for PnP Core SDK!

[MathijsVerbeeck]

@jansenbe I just thought about maybe adding some documentation/checks about the limitations (max 2gb/item, max 100 files and max 100gb in total) but al struggling about 'how' to check for the filesizes because that would mean that I'll have to retrieve every file and get the filesize of this file. This would generate quite a bit of traffic. Any suggestions on how to do this?

[jansenbe]

@MathijsVerbeeck : I would just do this via documentation. SDK users that want to enforce this can perform size checks in their code, enforcing this on every SDK user will be overkill for most use cases I think.

Just merged your PR, did a few tweaks but overall very good job done again! One thing that can trick contributors is the fact that the test project can access the internal classes from the SDK, so that's why I moved from ICopyMigrationOptions and an internal CopyMigrationOptions class to a public CopyMigrationOptions class. Other small change I did is ensuring the delay inbetween status checks is always configurable. Needed that to avoid having to wait during test cases.