Automatically quote all usernames in mentions that might require quoting

[initvector]

Usernames with spaces are automatically quoted when performing a mention. There are other usernames, like those with periods, which currently require quoting to be properly formatted, but aren't automatically quoted.

A couple possible solutions:

1. The requires_quotation check could be expanded to include additional characters.
2. The way mentions are formatted in posts could be more accommodating to these types of usernames.

[DaazKu]

Why aren't we just requiring quoting for all usernames that does not match /[^\w-]/.
We escape double quotes and we are done once and for all with that issue.