[WIP] add span to backpack button text

[pxpm]

reported in #5010

we could make developers life easier when they want to hide the button text and display only an icon by wrapping the button text in a span as suggested by @tabacitu

I've decided to create a class for each button type, eg: create-button-text-span, update-button-text-span. That way developers have the ability to hide only specific button texts, or hide all of them with *-button-text-span selector.