Unify units formatting across the app

[stackingsaunter]

Small changes to make app more consistent and a bit lighter:

• Use thin space as thousands separator for sats (for fiat too by default, unless we'll use system/language formatting there?)
• All sats amounts, regardless of the font size, should me "medium" weight (they're currently not eg. in main Wallet balance and transaction list). Exception: sats amount in tables and in other data structures, eg. tables in Node page or during opening channel flow (they stay "regular")
• When we introduce fiat amounts, they will be regular weight

[reneaaron]

We rely on system formats for formatting numbers for all locales, we can't (and shouldn't) override these locale specific things with some custom formatting. Have a look at e.g. India, Switzerland, etc. to get an idea of how different these things are handled around the world.

All sats amounts, regardless of the font size, should me "medium" weight

Agree here, we should be more consistent in that regard. Fixed it on the wallet page already, don't know what you exactly refer to when you mention "transaction list"?