feat: add custom context

[cqh963852]

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---

While we have multiple packages. Each package has it own locale. and i18n instance.

But useTranslation can't specify which context to be use.

This solution is inspired by react-redux.

[coveralls]

coverage: 96.013% (+0.03%) from 95.98% when pulling 922e318 on webzard-io:feat/context into 82fe572 on i18next:master.

[adrai]

https://github.com/i18next/react-i18next/tree/master/example/react-component-lib
https://react.i18next.com/latest/i18nextprovider#when-to-use