Apply signaling component -- rebase

[ActoryOu]

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Issue #, if available:

What was changed?

• Add Signaling component and coreJSON as external projects, and update Signaling code to call APIs of component.

Why was it changed?

• To apply Signaling re-factoring component into dev branch. Signaling component is separated out as independent library. And coreJSON is used in Signaling component.

How was it changed?

• Add Signaling component and coreJSON as external projects, import it via ExternalProject_Add, and update Signaling code to call APIs of component.

What testing was done for the changes?

• Verified master demo on Ubuntu
• Verified webrtc_client_test and pass all test cases.

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[codecov-commenter]

Codecov Report

Attention: Patch coverage is 96.20690% with 11 lines in your changes missing coverage. Please review.

Project coverage is 88.57%. Comparing base (3824226) to head (cd21c9d).

:exclamation: Current head cd21c9d differs from pull request most recent head f060c14

Please upload reports for the commit f060c14 to get more accurate results.

Files	Patch %	Lines
src/source/Signaling/LwsApiCalls.c	96.20%	11 Missing :warning:

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #2020      +/-   ##
===========================================
- Coverage    88.68%   88.57%   -0.11%     
===========================================
  Files           48       48              
  Lines        12726    12657      -69     
===========================================
- Hits         11286    11211      -75     
- Misses        1440     1446       +6     

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