Added Ukrainian NER and UD datasets

[lukasgarbas]

Added Ukrainian NER dataset from lang-uk project. Fixed splits (train and test) are taken from lang-uk/flair-ner:

from flair.datasets import NER_UKRAINIAN

corpus = NER_UKRAINIAN()

print(corpus)
# Corpus: 7886 train + 876 dev + 4045 test sentences

print(corpus.train[161])  # sentence example
# "І СхідSide втратив Дудка ..." → ["СхідSide"/ORG, "Дудка"/PERS]

And Ukrainian Universal Dependency Treebank from UniversalDependencies:

from flair.datasets import UD_UKRAINIAN

corpus = UD_UKRAINIAN()

print(corpus)
# Corpus: 5521 train + 673 dev + 898 test sentences

print(corpus.train[9])  # sentence example
# "Бо самою авторкою всі акценти розставлено зовсім очевидно." → ["Бо"/бо/SCONJ/Css/mark, ...

[lukasgarbas]

I also trained a few models on Ukrainian NER:

embeddings	method	parameters	dev F1 (micro)	test F1 (micro)
electra-base-ukrainian	fine_tune()	lr: 5e-5, batch: 16	95.02	88.39
Flair uk-forward, Flair uk-backward	train()	default	86.20	81.42
electra-base-ukrainian	train()	default, fine_tune: False, layers: 'all', layer_mean: True	92.87	87.38
electra-base-ukrainian, Flair uk-forward, Flair uk-backward	train()	default, fine_tune: False, layers: 'all', layer_mean: True	94.22	88.61

[alanakbik]

@lukasgarbas thanks for adding these datasets, and for posting these numbers!