Default Access Property Lists

[mkitti]

I would like a way to set the default access property lists at the package level.

Currently, when one needs a DatasetAccessProperties, it is constructed from scratch unless it is provided.

This can be a problem for high level methods where there is no opportunity to provide an access property list. For example when trying to use showtree and iterating through attributes.

My suggestion is that we create a method DefaultDatasetAccessProperties to provide the default properties and provide a way to access that.

For some properties, there is often an environment variable. However, setting this environment variable via Julia can be challenging for software using the C standard library, such as HDF5.