feat/fallback_stt

[NeonJarbas]

add the concept of fallback STT

this allows us to have a lower accuracy on device STT for when the remote STT fails, particularly useful during pairing stage

[codecov]

Codecov Report

Merging #77 (29c17e0) into dev (51814d2) will increase coverage by 1.46%.
The diff coverage is 51.82%.

@@            Coverage Diff             @@
##              dev      #77      +/-   ##
==========================================
+ Coverage   49.08%   50.54%   +1.46%     
==========================================
  Files         115      117       +2     
  Lines        9720     9915     +195     
==========================================
+ Hits         4771     5012     +241     
+ Misses       4949     4903      -46     

Impacted Files	Coverage Δ
mycroft/gui/service.py	0.00% <0.00%> (ø)
mycroft/skills/__main__.py	0.00% <0.00%> (ø)
mycroft/skills/intent_services/converse_service.py	58.97% <0.00%> (ø)
mycroft/gui/homescreen.py	38.54% <38.54%> (ø)
mycroft/gui/extensions.py	56.83% <56.83%> (ø)
mycroft/client/speech/listener.py	25.17% <59.37%> (+25.17%)	⬆️
mycroft/skills/skill_manager.py	57.44% <63.63%> (+1.05%)	⬆️
mycroft/gui/namespace.py	73.71% <68.18%> (+0.59%)	⬆️
mycroft/skills/mycroft_skill/mycroft_skill.py	72.02% <100.00%> (+0.03%)	⬆️
mycroft/stt/__init__.py	77.14% <100.00%> (+77.14%)	⬆️
... and 10 more

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