[RFR] Add error prop to FormHelperText, to mark it as error on error meta

[natrim]

Add's error prop to FormHelperText, to mark it as error on error meta

Makes the error text red (well, the error color defined by theme) like other errors in TextInput's

changes RichTextInput, RadioButtonGroupInput, CheckboxGroupInput and SelectArrayInput

note: added as pull to master instead of next as i consider it a bug that these components have inconsistent way to display error with other input's

edit: maybe i should add some borderBottom to make it even more consistent?
edit2: added images

before:

after (in this PR):

with borderBottom (not in this PR, shpuld i add it?):

[fzaninotto]

Nice! I don't think the border bottom is necessary in the Boolean input.

But this is a new feature, so as per our release policy, it must be PRed against the next branch rather than the master branch. Can you please rebase and repush?

[natrim]

@fzaninotto rebased on next

and btw this PR has nothing to do with Boolean input ? (the radios are RadioButtonGroupInput)

[fzaninotto]

Sorry, you're right, I meant RadioButtonGroupInput.

[fzaninotto]

Thanks!