Generalize RPC API to support other coins

[janoside]

In doing so, try to isolate BTC-specific code to more easily support other currencies in the future.

[dutchakdev]

I try change bitcoin adapter to litecoin, but have many errors with commands like getblockchaininfo, getnetworkinfo etc.

[janoside]

@dutchakdev After commit 70b28ff please try again. You can modify env.js to set "coin=LTC" (instead of the default "coin=BTC") and connect to your Litecoin node via RPC. Please let me know if you have problems.

[nicebbs]

TransactionsTrust Note
No address API is configured. See the example configuration file for help setting up an address API if desired.

[janoside]

@nicebbs This is referring to the BTCEXP_ADDRESS_API environment variable. You can set this to any of the values indicated in .env-sample. Note that each option has different privacy implications (running your own ElectrumX server will be more private than using any public website/API).