Support Swedish

[queleok]

[queleok]

https://spraakbanken.gu.se/en/resources/kelly
suggested source for gathering stats on letters frequency etc

[queleok]

• pick reasonable letter distributions (+notebook)
• support usage of wiktionary as validation backend ( Use wiktionary API for words validation #71 )
• enable switching between validation backends ( Use wiktionary API for words validation #71 )
• enable switching between languages
• add ref to spraakbanken on the index page