Split XTCE parser from packet_config

[ghost]

I didn't go all the way with the coverage in XTCEParser but I setup some frameworks for the future

[ghost]

closes #665

[codecov-io]

Codecov Report

Merging #664 into master will increase coverage by 2.33%.
The diff coverage is 63.14%.

@@            Coverage Diff             @@
##           master     #664      +/-   ##
==========================================
+ Coverage   83.52%   85.86%   +2.33%     
==========================================
  Files         153      154       +1     
  Lines       14364    14484     +120     
==========================================
+ Hits        11998    12437     +439     
+ Misses       2366     2047     -319

Impacted Files	Coverage Δ
lib/cosmos/packets/packet_item.rb	77.16% <100%> (+22.22%)	⬆️
lib/cosmos/packets/packet_config.rb	98.92% <100%> (+47.06%)	⬆️
lib/cosmos/packets/parsers/xtce_parser.rb	62.05% <62.05%> (ø)
lib/cosmos/tools/launcher/launcher_config.rb	96.74% <0%> (+1.62%)	⬆️
lib/cosmos/gui/qt.rb	37.03% <0%> (+1.74%)	⬆️
lib/cosmos/core_ext/string.rb	100% <0%> (+1.96%)	⬆️
lib/cosmos/config/config_parser.rb	92.38% <0%> (+3.08%)	⬆️
lib/cosmos.rb	93.1% <0%> (+3.44%)	⬆️
lib/cosmos/io/serial_driver.rb	92.85% <0%> (+3.57%)	⬆️
... and 7 more

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[ghost]

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