[NEW] Livechat features

[d-gubert]

Introduces components that enable apps to interact with the Livechat feature on Rocket.Chat.

Closes #122

[codecov]

Codecov Report

Merging #124 into beta will decrease coverage by 0.83%.
The diff coverage is 22.28%.

@@            Coverage Diff             @@
##             beta     #124      +/-   ##
==========================================
- Coverage   58.11%   57.28%   -0.84%     
==========================================
  Files          63       76      +13     
  Lines        2230     2505     +275     
  Branches      344      357      +13     
==========================================
+ Hits         1296     1435     +139     
- Misses        934     1070     +136

Impacted Files	Coverage Δ
src/server/bridges/AppBridges.ts	100% <ø> (ø)	⬆️
src/server/compiler/AppCompiler.ts	26.03% <ø> (ø)	⬆️
src/server/bridges/index.ts	100% <ø> (ø)
src/server/accessors/Reader.ts	100% <100%> (ø)	⬆️
src/server/managers/AppAccessorManager.ts	100% <100%> (ø)	⬆️
src/server/accessors/index.ts	100% <100%> (ø)
src/server/accessors/UploadRead.ts	22.22% <22.22%> (ø)
src/server/accessors/ModifyCreator.ts	72.13% <22.72%> (-27.87%)	⬇️
src/server/accessors/LivechatCreator.ts	25% <25%> (ø)
src/server/accessors/LivechatRead.ts	33.33% <33.33%> (ø)
... and 16 more

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