CU-8698mx1ua add two step linker

[mart-r]

This PR adds a 2-step linker.

The 2-step linker uses an extra step before dealing with CUIs directly.
Namely, it deals with Type IDs.

The approach uses the existing ContextModel to create context vectors for type IDs:

• It adds type IDs to the cdb.cui2info dict with a prefix for the key
• It uses a separate instance of ContextModel to add context vectors to TypeIDs during training

When doing unsupervised training:

• It checks all the possible TUIs for a given NER'd name
• If there's only 1 TUI, train on that
• If there's more than 1 TUI, trains the TUI(s) assigned to the CUI that is 'primary' for the NER'd name
• Only after that, refers to the regular linker to train the CUI

When doing supervised training:

• Trains for the TUI(s) assigned to the CUI that was annotated
• Refers to regular linker to train the CUI

When doing inference

• Narrows each entity down to the CUIs that correspond to the most likely type ID as per trained concept vectors
  • If the similarity is not good enough (as per the config), nothing is changed
  • If the most-likely type ID is determined, only CUIs that have that type ID are kept
• Refers to the regular linker to do inference on the (possible/hopefully) narrowed list of CUIs