[demo proposal] Twitter maxlength example with Validate system

[tlouisse]

Make an example with our validation/feedback system how to create a textarea that exceeds a certain amount of chars, with:

• warns about the amount of chars left
• warns about the amount of chars exceeded
• a custom (extra) validation-feedback outlet at a different location
• feedback will always be shown on keyup, regardless whether 'regular validation-feedback' has shown already
• style change based on whether exceeded/not exceeded
• a custom type like 'info-charcount'?