feat: modular lightning service, minor refactoring

[kincaidoneil]

• Simpler config (no Lightning pubkey or host required)
• Modular Lightning service
• Refactored to expose internal accounts (unfortunately necessary to expose balance to moneyd-esque clients)
• Balance logic updates (e.g., if two peers are misconfigured to both prefund, this prevents them from settling back and forth infinitely, or when they settle up, spitting money they've received right back)
• Copy some boilerplate from eth plugin
• Peering subprotocol changes/simplification to pubkey@host format (Lightning address)

Breaking: balance is represented differently in the store, the plugin configuration has been updated, and this version can't peer with prior versions of the plugin.

There will likely be subsequent minor breaking changes to support the connector refactor, after which we hope to preserve backwards compatibility.

[codecov-io]

Codecov Report

Merging #23 into master will increase coverage by 4.2%. The diff coverage is 83.09%.

@@            Coverage Diff            @@
##           master      #23     +/-   ##
=========================================
+ Coverage   75.38%   79.59%   +4.2%     
=========================================
  Files           6        6             
  Lines         390      392      +2     
  Branches       71       60     -11     
=========================================
+ Hits          294      312     +18     
+ Misses         61       50     -11     
+ Partials       35       30      -5

Impacted Files	Coverage Δ
src/utils/store.ts	80% <ø> (+36.41%)	:arrow_up:
src/plugins/server.ts	100% <100%> (+4.54%)	:arrow_up:
src/index.ts	70.58% <78.33%> (+2.89%)	:arrow_up:
src/lightning.ts	81.15% <81.15%> (ø)
src/account.ts	81.5% <85.1%> (+1.27%)	:arrow_up:
src/plugins/client.ts	84% <85.71%> (+8%)	:arrow_up:

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