Neutrino: Wallet

[manavdesai27]

This PR implements the wallet side of Neutrino, without getBlockPeer, as suggested by @pinheadmz

[codecov]

Codecov Report

Patch coverage: 69.23% and project coverage change: +0.02 🎉

Comparison is base (a4bf281) 70.26% compared to head (84aeb43) 70.28%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1166      +/-   ##
==========================================
+ Coverage   70.26%   70.28%   +0.02%     
==========================================
  Files         174      174              
  Lines       27367    27406      +39     
==========================================
+ Hits        19229    19263      +34     
- Misses       8138     8143       +5     

Impacted Files	Coverage Δ
lib/wallet/client.js	0.00% <0.00%> (ø)
lib/wallet/nullclient.js	87.50% <ø> (ø)
lib/wallet/nodeclient.js	71.87% <44.44%> (-8.13%)	⬇️
lib/wallet/walletdb.js	82.98% <79.31%> (-0.14%)	⬇️

... and 2 files with indirect coverage changes

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