[WIP] List benefits and button--input updates
Update height of .button--input and add left margin
Add missing small tick icon to sprite and fix positioning and size
Remove left margin on button--input
Add small arrow to sprite

For use in .list-benefits—sm.
Keep legacy .list--benefits class name to avoid any style issues

TODO Look to removing the .list--benefits class in the near future once
other repos have switched over to using the .list-benefits class
Add .icon--tick-sm KSS reference
Use $input-height for <input> and .button--input
Rename list-benefits--sm to -s to bring inline with size naming conventions

e.g. $mq-s
Update .button--input to .button--inline-input
Add KSS for button--inline-input
Merge pull request #84 from moneyadviceservice/list-input-button-email-signup

Add .list-benefits--s and .button--input