Consider highlighting validation messages in the main UI

[asbates]

When we gather and display validation errors in the main UI, consider making them stand out more. For example, we could follow the same pattern as with the inputs. Namely, red box with red text.

[gogonzo]

Some time ago we've implemented way to highlight div containing validation error in its children.

teal/inst/css/validation.css

Line 2 in cfc08c8

.teal_validated:has(.shiny-output-error) {

We move away from using shinyvalidate. We found simpler method to validate inputs