Fix Solutions i18n issues

@chrisndodge @muhhshoaib @martynjames : this fixes some i18n problems introduced in 
https://github.com/edx/edx-platform/commit/2cc0433833bee4ccfb4955bfdbbff0edc363920a

We need to be really careful with i18n, it causes me a lot of headache when stuff is improperly marked up for i18n, because I have to drop everything, deal with translators, and make PRs to fix strings. Please read through https://github.com/edx/edx-platform/blob/master/docs/en_us/developers/source/i18n.rst and ask me if you have any questions.
No, we definitely do this elsewhere. It was actually a request from translators that the "Sincerely" and "course team" lines appear in the same translation string because many languages have different sign offs depending on gender and/or singular v plural.