[RFC] [WIP] Support Realm.io as storage provider

[flagbug]

This PR adds realm.io as alternative to the SQLite storage provider.

This is an extremely rough implementation and currently doesn't even compile, because Realm doesn't support storing byte[] arrays yet.

I just wanted to get this PR so people can comment on it and see the progress.

//cc @paulcbetts @shiftkey @ghuntley @AndyDentFree who might be interested in this maybe?

[AndyDentFree]

Consider us extremely motivated by this PR and we're bumping the priority of adding the byte[] support.

[shiftkey]

Seems really interesting, especially on the mobile side of things.

@paulcbetts and I talked about benchmarking Akavache ages ago (I forget the specific context, there's probably a PR or two lying around), but I'd love to see how Realm stacks up against what sqlite is doing currently...

[flagbug]

@AndyDentFree 😍 😍 😍

I'm not extremely familiar with the Realm internals, but for SQLite we're using an OperationQueue to serialize and batch the requests to SQLite, for performance reasons. Does Realm exhibit similar characteristics, or can we just throw stuff at it™ and it figures out what to do?

@shiftkey Yeah, this is something I definitely want to do! A performance test suite would also be great to have for things like #285

[bmunkholm]

@flagbug Realm is 100% ACID. So when you do a commit() it is fully synchronous. It will fsync to disk twice to provide full serializable and crash safe writes. Only when the data has been written to disk safely will the commit return. Realm is really mostly optimized for queries as there are very physical limits to how much writes can be improved anyway.
The core does however have an alternative async mode where writes are basically handled in a queue and commit() will return before data is fully synced to disk, but otherwise it will write to disk as fast as possible. This mode is however not enabled yet in any of the products.

[anaisbetts]

Very cool @flagbug

[flagbug]

@AndyDentFree Do you, by any chance, have a rough estimate when the byte[] support will ship?

[AndyDentFree]

There will probably be a NuGet release some time next week. We will have it updated on our master on github well before then and I'll let you know if anyone here wants to grab from source.

[flagbug]

@AndyDentFree Awesome, thanks!

[flagbug]

Rebasing this onto akavache5-master

@shiftkey Pls implement PR branch switching thx 😿