Recommendation: Add variant parameter to BbThemeSwitcher

[garrenf]

Nothing too serious, but I would like to be able to change the variant of the BbThemeSwitcher for consistency. Right now, it is hard coded to Outline and can make the ui appear inconsistent.

[mathewtaylor]

Added in #363, now merged to develop. BbThemeSwitcher now has a Variant parameter (defaulting to ButtonVariant.Outline, so existing usage is unchanged) bound to the trigger button. This will ship in the next release.