Since it has been made superfluous by the IOManager API

* Added test for serialization of VolumeDataLayout objects
* Added a 'keys' vector to the MetadataContainer and added a MetadataType field to the keys to allow for ordered iteration through the metadata key/value pairs.
* Changed the AWS settings for test data to be CMake options instead of environment variables to make it work the same as locating test data.
* Added a getLayoutDescriptor() method to VolumeDataLayout and added some member variables to hold missing information about overall LOD settings.
* Fixed Base64Encode() functions and allow empty input to Base64Decode() function.

Don't build zlib on other platforms than windows as default since its
easier to just use the system zlib

Added DeserializeVolumeDataTest with test data for all compression methods except WaveletLossless. Renamed Rle to RLE as it is an abbreviation and not a word.

Made File class close the file in the destructor and removed the CloseGuard which isn't necessary anymore. Added asserts in File:open() to check that the file is not already open.

Added Base64Encode() function. Converted length parameter of Base64Encode/Decode()  to be 64-bit to allow large buffers since there is no point in limiting the low-level implementation.

Update JSON handling to conform to new version of OpenVDS specification. Rename everywhere 'Lod' to LOD since it is an abbreviation and not a word.

Made copyMargin/isCopyMarginNeeded internal functions take VolumeDataPageImpl pointers to remove the need for static_cast.

its in a non working state

Changed LodLevels enum to LODLevels and changed DimensionsND enum to be prefixed with Dimensions_ rather than using enum class.

stubbed out implementation

Changed Format enum to use '_' between the prefix (enum name) and the actual enumerated value. The reasoning is that this is intentionally not an 'enum class' and in this case the enum values are prefixed with the enum name which is made clear by the inclusion of the '_'. This change will match the coming changes to the JSON serialization.