Stepper form visual fixes

[richard-cox]

Fix two issues

#1584

• Stepper form styles were bleeding into list styles.
• Ensure top level styles stick to stepper level forms
• In the future this should be encapsulated in a form component

#1589

• Ensure we have a standard way of presenting and spacing the form inputs
• Previously a mat-select in a mat-form-field would double up its margin

[cfdreddbot]

Hey richard-cox!

Thanks for submitting this pull request! I'm here to inform the recipients of the pull request that you and the commit authors have already signed the CLA.