Simplify apply_models

[maxnoe]

In preparation of the addition of the disp reconstructors (and also the plugin system), I refactored the apply_models a bit to have already a list of reconstructors.

Right now, these are still loaded from the explicit path traitlets, not from a ComponentNameList(Reconstructor)

[codecov]

Codecov Report

Base: 92.75% // Head: 92.75% // Decreases project coverage by -0.00% ⚠️

Coverage data is based on head (cfc387c) compared to base (bae863c).
Patch coverage: 100.00% of modified lines in pull request are covered.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2113      +/-   ##
==========================================
- Coverage   92.75%   92.75%   -0.01%     
==========================================
  Files         214      214              
  Lines       17876    17865      -11     
==========================================
- Hits        16581    16570      -11     
  Misses       1295     1295              

Impacted Files	Coverage Δ
ctapipe/tools/apply_models.py	95.94% <100.00%> (-0.53%)	⬇️

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