Replace 'role="button"' elements with button elements

[mtgraham]

Is your feature request related to a problem? Please describe. We should specifically use button elements for elements that act as buttons.

Describe the solution you'd like

• Replace all div, span, etc. elements that serve as buttons with actual button elements.
• Create a less mixin for text only buttons (no borders or anything like that) so that we don't have to always override the system wide button styles anywhere we use this. This should ideally inherit whatever styles it can from its parent so that we don't need lots of button specific style overrides wherever we use buttons.

Describe alternatives you've considered Continue using role="button". We lose a bit of accessibility support without extra attributes applied to these elements though.