torchtext end-of-life and broken

[egpbos]

As noted in #827 and other recent PRs with breaking CI workflows, the torchtext package seems to be breaking down. It is no longer being developed (see https://github.com/pytorch/text/issues/2250).

Some options:

1. Find a workaround ourselves.
2. Look for a fork that is still maintained and switch to that.
3. Replace torchtext as a dependency.

Option 3 seems the most attractive to me, naively, but I haven't looked deeply into how unique the functionality is that we use. We only use torchtext in two ways:

• from torchtext.data import get_tokenizer in utils/tokenizer.py
• from torchtext.vocab import Vectors in test/utils.py, in a couple of notebooks and in the dashboard.

Can these easily be replaced? If not, a fourth option presents itself:

4. Cannibalize torchtext for these parts only.