Add yaml support

[n8maninger]

Adds support for a yaml configuration file similar to hostd and renterd.

directory: /etc/walletd
autoOpenWebUI: true
http:
  address: :9980
  password: sia is cool
consensus:
  network: mainnet
  gatewayAddress: :9981
  bootstrap: false
  enableUPnP: false
index:
  mode: partial # full, partial, none (full index will index the entire blockchain, partial will only index addresses that are registered in the wallet, none will treat the database as read-only and not index any new data)
  batchSize: 64 # max number of blocks to index at a time (increasing this will increase scan speed, but also increase memory and cpu usage)
log:
  level: info # global log level
  stdout:
    enabled: true # enable logging to stdout
    level: debug # override the global log level for stdout
    enableANSI: false
    format: human # human or JSON
  file:
    enabled: true # enable logging to a file
    level: debug # override the global log level for the file
    path: /var/log/walletd.log
    format: json # human or JSON