Implement registry change signaling

[sbidoul]

closes #40

[codecov-commenter]

Codecov Report

Merging #41 (b4ca949) into master (b65f976) will decrease coverage by 6.17%.
The diff coverage is 63.15%.

@@            Coverage Diff             @@
##           master      #41      +/-   ##
==========================================
- Coverage   83.85%   77.67%   -6.18%     
==========================================
  Files           6        6              
  Lines         223      224       +1     
  Branches       31       31              
==========================================
- Hits          187      174      -13     
- Misses         25       39      +14     
  Partials       11       11              

Impacted Files	Coverage Δ
click_odoo/env.py	56.09% <63.15%> (-16.41%)	⬇️
click_odoo/env_options.py	87.37% <0.00%> (-6.80%)	⬇️

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