[FEATURE] Specify button icon position

[esmeetewinkel]

What?
Want to be able to specify whether the icon on a button appears to the left or to the right of the button text. Also should be able to specify whether the text is left-aligned, right-aligned or centred.

Why?
Wants to be used by PLH Kids TZ deployment in nav_buttons template: web preview and sheet and issue

How?

• a new parameter icon_position which can be left or right
• ensure text_align parameter is interpreted when used in combination with the icon parameter (or maybe have text_position always be the opposite of icon_position)

Screenshots
Currently:

Desired:

(can ignore the primary rather than white button text, out of the scope of this issue)