Add msgctxt support for proper context in pot files
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Our `pot` files should use the `msgctxt` field to store context rather than prefixing the message. This will allow context to be rendered correctly in Crowdin.
Crowdin has a field beneath the string in the translation view where context is shown. It is always empty for GitLab because we don't use `msgctxt`
Reference: http://pology.nedohodnik.net/doc/user/en_US/ch-poformat.html#sec-podisamb
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