Add support for alternate currencies based on the tenant

[nerdenough]

This PR adds support to the boilerplate for multiple currencies, based on the tenant's settings. It adds a custom CurrencyValue component which builds on top of react-intl's FormattedNumber component and Intl.NumberFormat.

Examples

I couldn't find a way to change my language and currency through my account, but hardcoding both into the app gives decent examples.

Locale en, currency nok:

Locale nb-no, currency nok:

Locale en, currency nzd:

Locale en, currency btc:

Locale de, currency eur:

Notes

• I've currently locked react-intl to 3.0.0 due to Can't import the named export 'Component' from non EcmaScript module (only default export is available) formatjs/formatjs#1395.
• Probably need to look at better error handling and default local/currency if the tenant query fails.
• From what I can tell the Intl.NumberFormat functionality doesn't support special use cases like ,- for NOK or :- for SEK. When the locale is nb-NO and currency is NOK the currency will be rendered as kr 999,00. When the locale is en the currency will be rendered as NOK 999.00.
• The original VAT amount was vatAmount.toFixed(2). I have kept this value at 2dp for consistency but not sure if it's required.

[nerdenough]

Might need to leave the minimumFractionDigitals at its default (2dp for most currencies). Setting it to 0 results in values like this:

Whereas it would be more consistent to display like this:

[hakonkrogh]

Ideally, we would like the boilerplate to make one single request to the server to fetch all the data it needs for the first render. Performance FTW! This is why the existing query fetches the component data AND the top menu.

Can you move the query for fetching tenant info to the same query as well? And also, what kind of server timings are we getting if we do that?

[nerdenough]

Removing next-i18next in this PR as the removal depends on the CurrencyValue component as a replacement in some cases, which is required for #13.

[nerdenough]

Average timings (of 10):
Before: 6.4ms
After: 7.23ms