Fix loadData deprecations

[Sparks29032]

loadData is being deprecated, so we will need to update morph to use the new function signature.

To do this:

• Change all instances of loadData to load_data
• Make sure the requirements for diffpy.utils are the ones for the version where the deprecation is done. As such, hold off on this until near release of new morph version.
• Fix all function names in diffpy.morph. E.g. readPDF -> read_data.