[github-actions] add GitHub Actions

[wgtdkp]

This PR adds GitHub Actions.

• [X] Github Action yaml files.
• [X] rebase on PR https://github.com/openthread/ot-commissioner/pull/87 to fix Android build failure.

[codecov-io]

Codecov Report

Merging #96 into master will increase coverage by 0.10%. The diff coverage is n/a.

@@            Coverage Diff             @@
##           master      #96      +/-   ##
==========================================
+ Coverage   61.08%   61.18%   +0.10%     
==========================================
  Files          55       55              
  Lines        5381     5359      -22     
==========================================
- Hits         3287     3279       -8     
+ Misses       2094     2080      -14     

Impacted Files	Coverage Δ
include/commissioner/commissioner.hpp	30.76% <0.00%> (-69.24%)	:arrow_down:
src/library/commissioner_safe.cpp	62.24% <0.00%> (-0.87%)	:arrow_down:
src/library/joiner_session.hpp	62.50% <0.00%> (ø)
src/library/commissioner_impl.hpp	100.00% <0.00%> (ø)
src/library/commissioner_impl.cpp	62.02% <0.00%> (+0.12%)	:arrow_up:
src/library/joiner_session.cpp	86.55% <0.00%> (+0.58%)	:arrow_up:
src/app/commissioner_app.cpp	29.54% <0.00%> (+1.53%)	:arrow_up:
src/app/commissioner_app.hpp	80.00% <0.00%> (+5.00%)	:arrow_up:

[jwhui]

@wgtdkp , does this replace the need for Travis?

[wgtdkp]

@wgtdkp , does this replace the need for Travis?

@jwhui Yes, what about removing travis after merging github action?