Allow case-sensitive tagging

[julianlam]

This is only tangentially related to ActivityPub, but is more closely aligned with accessibility.

NodeBB currently lowercases tags, which I think might be because it's more easily searchable that way? Not sure.

Not surprisingly, it means those hashtags are mispronounced when read by screen readers. Camel cased words are distinguished phonetically, so if casing is preserved, then that should be ok.