Remove scene execution concurrency, fix camera issues & fix MQTT new value parsing

[Pierre-Gilles]

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Description of change

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[codecov]

Codecov Report

Merging #769 into master will increase coverage by 0.02%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #769      +/-   ##
==========================================
+ Coverage   92.36%   92.38%   +0.02%     
==========================================
  Files         419      419              
  Lines        5419     5422       +3     
==========================================
+ Hits         5005     5009       +4     
+ Misses        414      413       -1     

Flag	Coverage Δ
#server	92.38% <100.00%> (+0.02%)	⬆️

Impacted Files	Coverage Δ
server/lib/scene/index.js	100.00% <ø> (ø)
...r/services/mqtt/lib/handler/handleGladysMessage.js	100.00% <ø> (ø)
server/lib/index.js	94.20% <100.00%> (ø)
server/lib/system/index.js	100.00% <100.00%> (ø)
server/lib/system/system.init.js	100.00% <100.00%> (ø)
server/services/rtsp-camera/index.js	90.90% <100.00%> (+13.13%)	⬆️
server/services/rtsp-camera/lib/getImage.js	100.00% <100.00%> (ø)

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