MissionViewer fix and source file generation

[florentLutz]

This PR adds a feature and fixes a bug:

• With this commit, the issue with the MissionViewer not updating should be fixed. We now use of an Output widget https://ipywidgets.readthedocs.io/en/7.6.5/examples/Output%20Widget.html to isplay the FigureWidget. The widgets for selecting which value to display is the same. In addition to that it seemed that previously only the misson that was last added could be displayed in the viewer. Now a name can be added as an argument to the display method with the following rule : if no name is specified we take the mission added last and if the name is not recognized we raise an error.
• This PR also adds the "/source_file" folder as a component in the plugin system, much like the configuration file folder. Most of the command were adapted from what was done for the configuration file. This closes #474

[codecov[bot]]

Codecov Report

Merging #477 (9530612) into master (7fb9de6) will decrease coverage by 0.32%. The diff coverage is 74.48%.

:exclamation: Current head 9530612 differs from pull request most recent head b847d19. Consider uploading reports for the commit b847d19 to get more accurate results

@@            Coverage Diff             @@
##           master     #477      +/-   ##
==========================================
- Coverage   83.13%   82.81%   -0.32%     
==========================================
  Files         119      119              
  Lines        5253     5324      +71     
  Branches      811      828      +17     
==========================================
+ Hits         4367     4409      +42     
- Misses        739      767      +28     
- Partials      147      148       +1     

Impacted Files	Coverage Δ
src/fastoad/api.py	100.00% <ø> (ø)
src/fastoad/gui/mission_viewer.py	43.47% <12.00%> (-56.53%)	:arrow_down:
src/fastoad/module_management/_plugins.py	90.16% <89.65%> (-0.10%)	:arrow_down:
src/fastoad/cmd/api.py	92.30% <100.00%> (+0.58%)	:arrow_up:
src/fastoad/cmd/cli.py	86.31% <100.00%> (+1.60%)	:arrow_up:
src/fastoad/module_management/exceptions.py	100.00% <100.00%> (ø)

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[florentLutz]

did you check if the MissionViewer is able to show several missions, as it was before?

I did not checked how it looked like in FAST-OAD_CS25 and thought by looking at the code that only the first mission added would be displayed. Thinking that, I added a way to choose which mission to display, which was in fact unnecessary.

With this commit it does the same as before (with the update of the graph).

[florentLutz]

As you suggested, I changed all mention I could find of source file to source data file. The other big part in the latest commit is the refactoring of generate_configuration_file and generate_source_data_file. For both of them the function _generate_user_file is used (I used the term user file as a generic for configuration and source data file). I wonder if using an if/else statement depending on the type of user file is the right approach. Nonetheless, it has the merit of being clear but some lines could be spared by using a dictionary translating user file type into the associated functions (_list and _info)