New datatypes (UUID, Mixed, Set, Dictionary) integration branch

[fealebenpae]

The new round of data types are enabled in the v11 branch. The file format version has been bumped to 21 and the sync protocol version has been bumped to 3. The target version to release them is 11.0.0.

Please update your development branch's realm-core submodule to point to the new branch or start using the v11 alpha releases.