chore(ui): drastically simplify button components

[nickisnoble]

• Collapses our six different button primitives into one Button.tsx
• Drastically simplifies the API, relying on composition instead of injection to work with other components (like icons or hotkey hints)

Tip

This PR does a lot of renaming, here's the meat and potatoes:
https://github.com/macro-inc/macro/blob/nick/there-can-only-be-one-button/js/app/packages/ui/components/Button.tsx#L1-L76

[nickisnoble]

@sedson

Which do we like better for variants:

• 🅰️ Inline boolean <Button primary />
• 🅱️ Explicit prop <Button variant="primary" />

EDIT: Chose 🅱️. Less clever under the hood, more clear about what it is / does, intellisense, etc.

[nickisnoble]

Looks like there's a segfault during build?! cc @synoet

Could not recreate locally.

[synoet]

Re run the actions manually

[nickisnoble]

This is 80% renamings, but I did apply the new buttons to a few major surfaces:

• email/BaseInput
• SplitHeader
• Dock