Reviving H2, better cabin layout and double decker models

[ngomezve]

This PR is a revised version of PR #67, with changes made after the fuselage data revamping. In addition to the changes in 67, it fixes the conflicts with the H2 models.

From PR #67, it also introduces better design options if the fuselage layout has to be redesigned; for example, following a change in fuselage radius. The following changes are included:

• Adds a new cabin field to the fuselage struct, where the cabin-related parameters are stored. The relevant parameters are eliminated from parg.
• The seat height is included as an input parameter to ensure that seats can fit in the cabins.
• If the fuselage bubble has a downward shift, the floor is assumed to lie at the intersection of the two bubbles.
• If the fuselage has two decks, the decks are no longer assumed to be symmetric or have the same number of passengers. Instead, the number of passengers in the lower deck is optimized, along with the lower deck position if the cross section is circular. This optimization is subjected to constraints on cargo bay height and cabin height.
• A new function has been included to find the minimum radius required to have a given number of seats per row. This is useful if the radius has to be redesigned.
• The functions to size the cabin have been moved from IO to structures.

[codecov-commenter]

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Codecov Report

Attention: Patch coverage is 53.60000% with 116 lines in your changes missing coverage. Please review.

Project coverage is 73.32%. Comparing base (cb36835) to head (018c044).
Report is 22 commits behind head on main.

Files with missing lines	Patch %	Lines
src/structures/size_cabin.jl	48.93%	72 Missing ⚠️
src/structures/update_fuse.jl	46.15%	28 Missing ⚠️
src/IO/save_model.jl	0.00%	12 Missing ⚠️
src/balance/balance.jl	33.33%	2 Missing ⚠️
src/IO/outputs.jl	96.77%	1 Missing ⚠️
src/IO/read_input.jl	83.33%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #78      +/-   ##
==========================================
+ Coverage   71.88%   73.32%   +1.43%     
==========================================
  Files          77       77              
  Lines       13684    13846     +162     
==========================================
+ Hits         9837    10152     +315     
+ Misses       3847     3694     -153     

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