Login error message needs improvement

[QuantumTux]

Blank spaces are not permitted in Horizon User Names - in and of itself, that is not a problem

In the event a user, when attempting to login to the Horizon web interface, accidentally inserts a blank space into their User Name, the error message is a cryptic Invalid credentials

The error message should be clearer, perhaps something like Invalid User Name - Spaces not permitted

That would give actionable feedback to the user, and is easy enough to check.