Standardize numbering for coins

[Varunram]

Right now, we use pretty much arbitrary numbers (1,257, 65535), etc. We must have some sort of code / way we handle new alts (eg monotonous increment of numbers based on first alt added, choose your number and wait for consensus, etc). Or we could use SLIP173 types everywhere (however, that'd mean changing the type of CoinType)

[delbonis]

I think it is better to use name-based coin types like SLIP173. It would make the UX easier to understand.