Don't restrict typing in name fields to valid characters

[david-crespo]

Added in #2512, tweaked in #2549.

Issues raised by @taspelund and @cbiffle in chat:

1. No way to know what the rules are if you can't submit something invalid and see the error (see also Add tooltip or hint to name fields with requirements #1792)
2. Very confusing that you can type - sometimes (after other characters) but not other times (when field is empty)
3. Pasting something with invalid characters filters those out but leave the rest, so you can end up with a different name than you thought if you're not paying close attention