CU-869805t7e alt names fixes

[mart-r]

Fix some alternative name stuff:

• Separate the picking of appropriate category name
• Select category name correctly when using the MetaCAT.eval method
• Fix usage of alternative_class_names when encoding category names
  • I.e use the correct class name rather than the list of the class name as a key in category_value2id
• Some other minor changes
  • Lowering indentation
  • Removing duplicate exceptions

[tomolopolis]

Task linked: CU-869805t7e MetaCAT alternative name fixes

[shubham-s-agarwal]

lgtm!