[EN] Add variant for verbs and adjectives

[BoboTiG]

https://en.wiktionary.org/wiki/memoises uses a template we are not yet handling: en-third-person singular of. When checking our code, it appears we are partly ignoring verbs: https://github.com/BoboTiG/ebook-reader-dict/blob/47125f12d939aa766ea4a2d5d05ccb840584be65/wikidict/lang/en/init.py#L40-L41

And partly rendering them: https://github.com/BoboTiG/ebook-reader-dict/blob/47125f12d939aa766ea4a2d5d05ccb840584be65/wikidict/lang/en/init.py#L105-L110 (and more lines around)

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Same question for plurals. Those are ignored in French. But verbs and plurals were not really handled in other locales because of lack of support.

Finally, what should we do?

[BoboTiG]

I read an english book on the Kobo, and variants were missed a lot. Let's add them!