feat(web): implement stdout support

[lupino3]

Contributes to Web UI: basic SYSCALL support #1224
Also add a simpler example program.

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 13 lines in your changes missing coverage. Please review.

Project coverage is 52.49%. Comparing base (0ad2bbf) to head (f2a7f77).
Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
src/main/java/org/edumips64/client/Simulator.java	0.00%	7 Missing ⚠️
.../main/java/org/edumips64/client/ResultFactory.java	0.00%	4 Missing ⚠️
src/main/java/org/edumips64/client/Result.java	0.00%	2 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #1228      +/-   ##
============================================
- Coverage     52.53%   52.49%   -0.04%     
  Complexity     1468     1468              
============================================
  Files           252      252              
  Lines         10214    10221       +7     
  Branches       1102     1102              
============================================
  Hits           5366     5366              
- Misses         4525     4532       +7     
  Partials        323      323              

Files with missing lines	Coverage Δ
src/main/java/org/edumips64/client/Result.java	0.00% <0.00%> (ø)
.../main/java/org/edumips64/client/ResultFactory.java	0.00% <0.00%> (ø)
src/main/java/org/edumips64/client/Simulator.java	0.00% <0.00%> (ø)

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