Reduce memory impact of loading entire dictionaries into memory

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Right now dictionaries are not buffered, but are rather read in their entirety before being used to instantiate a User:

Offending helper method that reads dictionaries.

Here the result is used to instantiate a User.

This is a massive resource hit and could likely be done better but I'm not quite sure how. Hopefully we don't need to wait until the web-extensions API exposes the actual browser spell checker (which would remove the need for nspell entirely) but that may be the case.