Update TrustChain validation, refactor packet serialization

[MattSkala]

• Add block public key and signature validation
• Add chain consistency validation
• Refactor packet serialization to reduce boilerplate
• Store WAN and LAN address for verified peers for more reliable LAN introduction

[codecov]

Codecov Report

Merging #9 into master will increase coverage by 0.56%.
The diff coverage is n/a.

@@             Coverage Diff              @@
##             master       #9      +/-   ##
============================================
+ Coverage     75.88%   76.45%   +0.56%     
- Complexity      438      465      +27     
============================================
  Files            53       54       +1     
  Lines          1783     1792       +9     
  Branches        225      239      +14     
============================================
+ Hits           1353     1370      +17     
+ Misses          293      276      -17     
- Partials        137      146       +9     

Impacted Files	Coverage Δ	Complexity Δ
...in/java/nl/tudelft/ipv8/keyvault/CryptoProvider.kt	66.66% <0.00%> (ø)	0.00% <0.00%> (?%)
...ipv8/attestation/trustchain/TrustChainCommunity.kt	34.06% <0.00%> (+0.59%)	33.00% <0.00%> (+2.00%)	⬇️
ipv8/src/main/java/nl/tudelft/ipv8/Community.kt	78.45% <0.00%> (-0.05%)	52.00% <0.00%> (+7.00%)
...lft/ipv8/attestation/trustchain/TrustChainBlock.kt	64.96% <0.00%> (+0.20%)	45.00% <0.00%> (+13.00%)	⬇️
ipv8/src/main/java/nl/tudelft/ipv8/IPv8.kt	74.00% <0.00%> (+6.00%)	9.00% <0.00%> (+1.00%)	⬇️
.../src/main/java/nl/tudelft/ipv8/messaging/Packet.kt	92.00% <0.00%> (+32.00%)	7.00% <0.00%> (+2.00%)	⬇️

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