Extract currency bundle

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | yes
| BC breaks?    | no
| Deprecations? | no
| Fixed tickets | -
| License       | MIT
| Doc PR        | -

Money should be only about money processing, especially that we use it in other bundles. I thought that extracting a CurrencyBundle and renaming the Money component to Currency makes sense.

Especially that we need more stuff, the base CurrencyContextInterface now lives in the component etc.

Services for updating exchange rates will follow soon, I need to do few tweaks.

Quick summary, cause I'm tired tonight:

- Money bundle cares only about money formatting and forms.
- ExchangeRate renamed to Currency and moved to CurrencyBundle.
- Introduced CurrencyProviderInterface and appropriate service.
- Money component renamed to Currency.