Support TF2, Python 3 and config switching off context embeddings

[amir-zeldes]

• Supports TF2.2 using tf.compat.v1
• Use Python 3-compatible syntax
• Use lm_path = none to switch off contextualized embeddings for low resource languages
• Support word embeddings files with header row (vocab size, dimensionality in first row)
• Bug fix in entity type breakdown in final eval report