Rename SettingDescriptor's type to setting_type

[rytilahti]

This makes the type of 'type' consistent among all descriptors.

[codecov-commenter]

Codecov Report

Merging #1715 (466ae9a) into master (7ad548a) will decrease coverage by 0.02%.
The diff coverage is 61.11%.

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@@            Coverage Diff             @@
##           master    #1715      +/-   ##
==========================================
- Coverage   81.82%   81.81%   -0.02%     
==========================================
  Files         193      193              
  Lines       17987    17990       +3     
  Branches     3846     3847       +1     
==========================================
  Hits        14718    14718              
- Misses       2982     2984       +2     
- Partials      287      288       +1     

Impacted Files	Coverage Δ
miio/miot_models.py	63.63% <ø> (ø)
miio/device.py	83.90% <25.00%> (-1.48%)	⬇️
miio/descriptors.py	96.36% <90.00%> (ø)

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