[MP-1010] Fix ampersand in email_subject_room_name

[dasha140132]

No description provided.

[nmagedman]

Thank you, but this doesn't feel like it's the right approach. We have a mixing of concerns (both in upstream's code and in this patch) where replacekey (and by extension replace) is doing two unrelated things:

1. It is expanding placeholders in a template string.
2. It is HTML-escaping the template values.

I prefer that we separate these concerns. replace/replacekeys should only do text substitution. The caller should handle any escaping before passing in data/value. If needed, we can have another helper function that escapes all the values in an object, which we could compose with replace().