Cleaned up and simplified the Blob layer

- removed things that are not in the original python layer
- removed all upload/download methods because the Blob layer does not offer transactional guarantees on very big data
- fail if size is negative
- flow the CancellationToken everywhere
Cleaned up the String Interning layer

- Moved to "FoundationDB.Layers.Interning" namespace
- fixed a few bugs, made it more thread safe
- Added transactionals
- Flow the CancellationToken everywhere
Added a unit test to validate that GetRange([0, 100), limit=1) would conflict with a Set(...) or not, depending on if the result of the GetRange would change or stay the same.
Merge branch 'master' of https://github.com/Doxense/foundationdb-dotnet-client