Safer plugin import

Created by: stefanoborini

First implementation and change of API to make the plugin import system more robust against broken plugins.

This PR requires we readapt all plugins. Similar changes are required also for the other classes API so that it's uniform.

Created by: codecov[bot]

Codecov Report

Merging #129 into master will decrease coverage by 0.78%. The diff coverage is 77.14%.

@@            Coverage Diff            @@
##           master    #129      +/-   ##
=========================================
- Coverage   93.49%   92.7%   -0.79%     
=========================================
  Files          36      36              
  Lines         722     754      +32     
  Branches       58      63       +5     
=========================================
+ Hits          675     699      +24     
- Misses         40      48       +8     
  Partials        7       7

Impacted Files	Coverage Δ
force_bdss/api.py	100% <100%> (ø)
force_bdss/base_extension_plugin.py	81.81% <76.47%> (-18.19%)

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