Unit tests and improvements to settings change callback

[NeonDaniel]

Refactor _handle_settings_file_change to ignore non-settings file changes
Add unit tests for settings filewatcher and file change callback
Potentially closes #91

[codecov]

Codecov Report

Merging #116 (3bf453c) into dev (0cdf027) will increase coverage by 58.66%.
The diff coverage is 79.25%.

@@            Coverage Diff             @@
##             dev     #116       +/-   ##
==========================================
+ Coverage   0.00%   58.66%   +58.66%     
==========================================
  Files         33       33               
  Lines       3173     3242       +69     
==========================================
+ Hits           0     1902     +1902     
+ Misses      3173     1340     -1833     

Impacted Files	Coverage Δ
ovos_workshop/decorators/converse.py	0.00% <0.00%> (ø)
ovos_workshop/decorators/fallback_handler.py	0.00% <0.00%> (ø)
ovos_workshop/skills/active.py	100.00% <ø> (+100.00%)	⬆️
ovos_workshop/skills/decorators/__init__.py	0.00% <0.00%> (ø)
ovos_workshop/skills/decorators/converse.py	0.00% <0.00%> (ø)
...vos_workshop/skills/decorators/fallback_handler.py	0.00% <0.00%> (ø)
ovos_workshop/skills/decorators/killable.py	0.00% <0.00%> (ø)
ovos_workshop/skills/decorators/layers.py	0.00% <0.00%> (ø)
ovos_workshop/skills/decorators/ocp.py	0.00% <0.00%> (ø)
ovos_workshop/skills/intent_provider.py	0.00% <0.00%> (ø)
... and 18 more

... and 4 files with indirect coverage changes